How does Windows Live Sync stack up to DropBox?
So how do the two services match up? Let's take a gander.
Capactiy: tie (sorta)
Both Dropbox and Live Sync provide 2GB of accessible-by-anyone cloud storage for free. Dropbox, of course, offers paid upgrades while Live Sync presently does not. Whether Microsoft will allow you to expand into more of your SkyDrive's maximum 25GB of space remains to be seen.
Flexibility: Live Sync
Though Dropbox lets you choose which subfolders of your My Dropbox folder you want to sync, there's no easy way to include folders located elsewhere on your system (yes, there are ways to do it using symlinks). Live Sync lets you choose any folder on your system, plus it can also sync Internet Explorer Favorites and Office templates.
Peer-to-Peer Sync: Live Sync
Dropbox doesn't offer this function, and it can be incredibly handy. In addition to letting you sync 2GB of data to your SkyDrive cloud storage, Live Sync will also do folder-to-folder syncing on any machines you want to connect. Just sign in with your Live ID on both systems and create the folder pair.
Platform support: Dropbox
With apps available for just about every mobile device around and desktop versions for Windows, Mac and Linux, Dropbox has a clear advantage here. Live Sync will probably get a Mac client, but mobile access will likely be limited to the browser on non-Windows Phone 7 devices.
My ISP is pretty stingy with the uploads -- I'm limited to about 34K/s, and my downstream gets choked whenever I approach that limit. As such, I prefer apps that provide an option to limit transfer speeds. Dropbox does, Live Sync doesn't.
This isn't to say that Live Sync is a hog. I never noticed any issues with my connection while running a sync operation, but I prefer being able to set a self-imposed limit.
Remote access: Live Sync
This may not factor in to the decision-making process for you, but if you're a Windows user and you think having full remote access to your computer might come in handy from time to time, Live Sync can do it and Dropbox can't. Even if you don't think it's a feature you would use often, there's always a chance that one day you'll need access to some file you've forgotten to sync -- and Live Sync's remote function will be a life-saver.
If upgradeable storage and cross-platform (including mobile) support are crucial, go with Dropbox. If you're primarily concerned with accessing files on your Windows systems both at home and at work, Live Sync is tough to beat with its peer-to-peer sync and remoting options.