Now that I've been using Dropbox and Live Mesh for a while, I can offer a brief comparison between the two.  They are both great and I've found a good use for them both, but they each have their strengths and their weaknesses.

My overall assessment is that I like Live Mesh for all its features and flexibility in folder structure, and I like Dropbox for its simplicity, speed, and reliability - it just works.

Dropbox (free version)	Live Mesh
It's free!	It's free!
Quick to synchronize files between local and online version	Slow to synchronize files between local and online version
2 GB storage free - plenty but less than Live Mesh	5 GB storage free
Works on Windows, Mac, and Linux	Doesn't work on Linux (yet)
Doesn't let you specify folders other than "My Dropbox"	Flexible in the folders you can synchronize
Synchronizes all folders locally on all computers	Lets you choose which folders to synchronize locally, and where
Lets you connect through a proxy	Uses Internet Explorer's connectivity settings, so if you specify a proxy there Live Mesh will use it  No option to connect through a proxy
Free extra storage for referring new users	No referral program for extra storage
No remote control feature	Lets you control other connected computers remotely
No drag-and-drop between online and local storage	Drag-and-drop between online and local storage (not yet functional)