SLEAV  I'll second both the review and the other comment about it...

I like Things. I wanted to LOVE things. But I can't. Things has amazing potential, but the overview for me is it isn't there yet. I bought all the apps, and now have it shelved until it's truly cloud-capable. Trying to do mac-to-mac syncs results in crazy-making duplicates - I've tried several ways to solve this.

And I'll also concur about the desolate state of GTD implementation on Mac. This just simply amazes me. And hey - nevermind GTD! Let's say you just want a really good, reliable to-do list that'll sync across several Macs and iPhone or cellphone - you're flat out of luck. I know - I have them all. RemembertheMilk, ToodleDo, ToDo, ToDo's, iCal+Apple Mail (whose bright idea was that - putting tasks in with the mail?). Heck, I'd settle for the functionality that came with my old Palm.

At this point, I've settled into OmniFocus - which cost a boodle to do both the Mac version and the iPhone as well - but it's the best (so far) at solving the problem for me. Steep learning curve, and it's like using a steam roller to make pie crust, but at least it works.  
(Version 1.1.3)

SLEAV  SugarSync does indeed work well - and it works quickly.

I could wholeheartedly recommend it without reservation if it weren't for the glaring problems of data loss caused by SugarSync's servers' inability to handle certain Mac-only files (those that contain resource forks).

And it's not that SugarSync (or anyone using Windows Server 2003/2008 or Linux server software) is unique in this regard. My complaint is that warnings concerning very serious data loss are not conspicuously noted on SugarSync's website or in their guides and ReadMe files.

Examples:

.webloc files - these URL files, created by either saving a URL or dragging a web browser bookmark on to a folder, are often rendered empty (Zero K) once saved, backed up, sync'd with a different Mac and re-opened.

.textclipping - these clipping files are rendered empty (Zero K), same as above

.qdfm - Quicken data - sync'ing sometimes leaves these Quicken data files corrupted, resulting in total data loss - Quicken users, beware!

.pages - SugarSync can corrupt a Pages file once it is saved, sync'd, opened in a different Mac, and saved again - resulting in partial data loss (also true for Keynote files)

.domain and .domain2 - iWeb files, same as Pages files above

Is this unique to SugarSync? No! Dropbox exhibits the same behavior.

Alternatives?

In my tests, JungleDisk handles Mac files properly - but does not provide near the functionality of SugarSync.

MobileMe - well, if they didn't handle Mac files properly, what's the point? But using iDisk to sync and backup a lot of content from different Macs is like watching a slug read a James Joyce novel.

Mozy.com - Mozy seems to handle Mac files properly, but again, there is a sacrifice in usability.

My solution? So far, it has been to remember that URLs (.webloc files), text clippings, and Mac-unique file formats are going to get trashed - and to ZIP them before saving them. SugarSync seems to handle the resource-laden Mac files fine if they are .zipped (and obviously, one doesn't make "incremental" versions of .zipped files - you save one, open it, trash it, and re-zip it.

Also, SugarSync's pricing structure is reasonable, even for large data sets.  
(Version 1.6.2b)