TOMIS  "does not encrypt your very personal data" [citation needed]

If you're going to make a potentially inflamatory statement like this, please provide your evidence to support it.

In fact at http://fruux.com/faq/read/items/is-my-data-safe/ they state that: "fruux uses industry standard SSL encryption (like your bank does for your homebanking)"

However, I can find nothing to support or disprove the idea that data is stored on-disk on their servers in an unencrypted manner.  
(Version 0.9.6.5)

MACED  they state everywhere that the data IS encrypted and the part you cited basically says that they wont give it to anyone, unless they are forced by the law. even if they hadn't written it down in their policy, they had to comply with the government.

thats perfectly ok. if you buy something at amazon (or your local bookshop), they also wont tell anyone that you just bought a book about chemistry (or whatever), unless you blow up some government building with your new skills and then the police (or some other government body legally) forces amazon (or your local bookshop) to tell them who bought chemistry books during the last weeks.  
(Version 0.9.6.6)

TOMMY_B  I love fruux & trust them implicitly...

it's funny the OP made no mention of a much more relevant subject: the physical location of where the data is stored, which is outside of the US. If one had reason to give pause in trying fruux out, that would be it (if you live in the US that is), not this other foolishness that is par for the course.  
(Version 0.9.6.6)

MACED  I guess the physical location is also a non issue. AFAIK fruux uses Amazon Webservices infrastructure like Dropbox. Even if the data would be located in Europe (be in an european datacenter of Amazon or elsewhere) I don't see any issue with it. As far as I know european data protection rights are much stricter then in the US.  
(Version 0.9.6.6)

MISHA  Fixed now.  
(Version 0.9.6.4)

FENRISULF  Tiger was released in 2005. (I stood in line for mine). It works on my PPC Mac to this day, as Leopard isn't all that "grand" on PPC's (being a dead architecture at this point...) I do not know what Fruux has that requires Leopard, but it most likely is something that the Tiger libraries do not have. Saying that Tiger's obsolete based on the date of Leopard's release is really not how to view it. Leopard is taking the spot from Tiger (faster/slower.. depends) and as Leopard becomes the dominant OS, Tiger loses "cutting edge" support.

Tell the Windows 2000 people about XP's draining of life from their perfectly good OS (and 2000/XP were more similar than Tiger/Leopard are....)

Time marches on... My PPC Mac G5 is 6(?) years old. My G4 is 11. They both work fine and will for many years to come... albeit my G4 runs Panther... I think I'll switch it to PPC linux one day soon. But I don't consider developers supporting Leopard only as "ready to abandon" a user when the "next big OS" comes out. It's not like the current version you may be running suddenly dies on you when the developer releases for 10.7. It's all about perspective.  
(Version 0.9.6.1)

SESQUIPEDALIAN  PENGUIRL "... OS of choice ..."

Exactly. You've made your choice. You choose not to use the minimum level OS that is required for this software. That's fine, and godspeed to you. But choices have consequences. The consequence of your choice is that you can't run fruux. Those of use who choose to run 10.5 or higher can consequently run fruux. That's just how the world works. There's really nothing else to discuss.  
(Version 0.9.6.2)

A_PROMPT  Quite a realistic point of view. I suggest you tried SyncMate for synchronzation. It's free and possesses a number of useful features, supports Tiger, Leopard and Snow Leopard. This freeware may appear helpful.   
(Version 0.9.6.4)

SESQUIPEDALIAN  Many of the forms of data fruux syncs is implemented completely differently in Leopard than it was in Tiger. The fruux team would have to write what would amount to an entirely new application in order to work with Tiger.

So in effect what you are saying to the developers is "Hey, you guys should reduplicate all the many man-hours of work you've done so that you can cater to my refusal to meet the system requirements of your software. Clearly your time and energy are so worthless compared to mine that I think you should do this—for free—so that I don't need to spend any money on anything."  
(Version 0.9.6)

PENGUIRL  No that is not what I'm saying, that is what you choose to see. What I'm saying is that if a developer chooses to support only one version of an OS, then it's very possible that someone could come to rely on your product only to get left behind when the next OS upgrade comes out 18 months later. It has nothing to do with refusing to meet the system requirements of your software. I freely choose not to run Leopard because it is bloated, inefficient compared to Tiger, and I am in the exact reverse scenario I just described with CS 2 Premium. If I could go straight to Snow Leopard I would but CS 2 Premium runs poorly in Rosetta, if it would run on 10.6 at all.

If you choose not to support Tiger, that's your free choice. However it makes me leery of ever using any of your products, free or not. If you have an issue with that, so be it. I really don't care.  
(Version 0.9.6)

SESQUIPEDALIAN  It's not my software. I have nothing to do with it. Heck, I've never even used it. Under no circumstances should my comments be in any way attributed to the developers of fruux.

Now, in full recognition that I am just some random person whose views are semi-educated but authoritative for nothing:

I doubt fruux will face major problems regarding forward compatibility any time soon. 10.6 continues with the same system used in 10.5. If 10.7 introduces any changes, the fruux team will have access to developer betas of it long before end users, and will therefore have time to implement compatible changes as necessary.

The only way to kill fruux going forward would be if Apple removed the Sync Services API, thereby cutting off all third party access to syncing. The chances of that are close to zero.

If changes to, say, the iCal format are introduced in 10.7 or later, fruux may have to be updated to deal with the new formatting. That would not be trivial, but it would be doable. And there would be motivation to do it, because the new format would be adopted by many.

Going back to support obsolete formats, on the other hand, is not very worthwhile, since they have a dwindling user base. Your own comment, for example, would seem to indicate that you are likely to upgrade once 10.6 comes out, or if not, 10.7.  
(Version 0.9.6)

VEGGIEDUDE  "if a developer chooses to support only one version of an OS, then it's very possible that someone could come to rely on your product only to get left behind when the next OS upgrade comes out 18 months later"

This software was developed when Leopard was the current OS. There is no indication to think they will leave behind Leopard users 18 months from now.  
(Version 0.9.6.1)