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.
.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.
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.