I just installed it but I still don't see such possibility.
You can choose only folders that you want to sync from DB to your computer, but you can't choose the folders that you want to sync from your PC to DB...
You can, but not directly: I sync my documents and pictures folders (among others) into Dropbox. There are two ways of doing this. The first is the way I did it and that's to move the folders under dropbox and then create symlinks back to the original location (so my ~/Documents folder is actually a symlink to ~/Dropbox/Documents)
The other way is to create a symlink within your dropbox folder to point to the folder you want including (so you'd have ~/Dropbox/Documents which is a symlink to ~/Documents)
I agree that it would be better if Dropbox allowed you to arbitrarily sync any folder, but until that functionality is there, the symlink option works well once you have it set up
And, in answer to the OP's question, Dropbox is superior to MobileMe iDisk in every conceivable way: It's
much faster, cross-platform, more flexible (you can share any folder with other users, or create a shareable link to any file or folder), include file versioning (30 days of versions available for no extra charge) and will rapidly become a vital part of your computing setup. I can't recommend it highly enough!
Here's an example of how we use Dropbox: We do a bit of web hosting (nothing on a grand scale), and before Dropbox, we had FTP access to our server for our customers. Now, with Dropbox we just create a shared folder for each of the websites and grant access to that folder to the customer. All they have to do now is update their local copy of the website within Dropbox and it is automatically published to the server. It's easy for customers to understand, it gives them a cloud backup of their site and versioning and it means we could turn off FTP on our server (which is always an open invite for people to try and hack the server). Try doing that with MobileMe iDisk...