AKROBAT  I'm envious of those that were able to get this to work. I tried countless times and finally deleted the thing.  
(Version 1.4)

CRATER  Great stuff! It did take me a while to get everything set up and working but it syncs perfectly now.

I have 5 iCal calendars syncing with 5 google calendars. The issues I had were 'failing to create sync session' and inability to 'update google calendar' (or something like that).

Once I switched to normal syncing for all calendars and did the whole resetting thing (i.e reset iSync & gSync, log out and back in) it worked great. The was one problem in that resetting gSync does not seem to remove all of gsync's files from the hard drive, specifically files in ~/Library . I had to manually remove those to sort out the problems. All users should make sure to back up their calendars before messing around.

In general, this is a great app and once I've used the demo for long enough, my £10 will be on it's way. good work.  
(Version 1.2.1)

TUNT  Somewhat too expensive, but cheaper than a .mac account. It's working fine for me!  
(Version 1.2.1)

LOTUS49  I came looking for this because I was previously using gcaldaemon (which worked but was NOT easy to setup) and that doesn't work with Leopard. Spanning Sync is too expensive and I don't like the unnecessary use of an external server.

GSync did the trick for me. I haven't tested it extensively but it was easy to setup and seems to have synced my calendars properly. My tenner is on its way.  
(Version 1.2.1)

M CHANG  Running OS 10.4.10 (home) and 10.4.11 (work). Both systems are syncing quite happily with my Google Calendar. Program does what it's supposed to. There are some items that aren't explained in the Help (hence my 4 out of 5 rating).  
(Version 1.2.1)

DEBTMAN7  Well let me give a positive review here. I just tried the 1.1.2 release with leopard and so far with a few trials I am extremely happy. As long as it holds up and I don't encounter any problems, I'll be buying it.

Why? The alternative, Spanning Sync, costs 3 times as much. The free alternative, GCalDaemon, doesn't work with leopard and even if it did, it does not support subscribed private iCal's (i.e. my wife shared her calendar with me through google calendar, but GCalDaemon can't sync that). The free service plaxo can sync multiple calendars, but through my testing only syncs them with their own calendar and not with each other (so you can't sync iCal with google calendar, though you can sync them all with plaxo).

So far this one just worked. Can't beat that.  
(Version 1.1.2b)

JIMFULLERATMACNESS  I think this review is a little harsh.... the Leopard release changed both Apple iCal and Apple Sync Services.

Also testing at large scale could only happen once Leopard shipped.

We try to support the best we can and we believe that the latest BETA has solved all issues with Leopard and duplicates.

cheers, Jim Fuller  
(Version 1.1.2b)

VANILLAICEE  This is a horribly supported product which I recommend people not even try to run. If you chose to you will only be frustrated and end up beta testing software that should not be released to the public.

The current version (in Leopard) will duplicate your all day events and improperly handles sync conflicts. The developer does not seem to prioritize testing before releases. Unfortunately GCALDaemon is not 100% in Leopard so I can't recommend that instead, but this program is not a solution for bidirectional syncing. Hopefully Google will release CalDAV compatibility soon and this program can die.  
(Version 1.1.1b)

SONICDEVIANT  For those among you who are more tech savvy (i.e., you're not afraid of the Terminal), give GCALDaemon a try. Works great and is FREE!  
(Version 1.1b)

RAMONYCAJAL  I have been using gSync for some time now, and have experienced nothing but frustration. Synching is erratic, with problems occurring sporadically and unpredictably. Problems include: duplicate entries, entries that disappear from the Google calendar following a sync, and unwanted invitations that appear in all recurring events. I have downloaded a demo of SpanningSync, and so far it has worked without fail. I recognize the shortcoming of SpanningSyc (price, use of their server), however, in addition to the absence of bugs, they have the added advantages that they handle recurring events, they sync alarms correctly, and they perform scheduled syncs in the background; gSync offers none of the above. The gSync website continues to mislead by headlining the claim "duplicates and recurrences solved"; this is not the case. Multiple users have been posting complaints on the developer's Google Group, but fixes are yet to appear (the developers lay the blame at Google's doorstep). In sum, this application is certainly not ready for prime time.  
(Version 1.0.4)