Crashplan and Dropbox are two totally different things. Crashplan is an online storage and backup with all the bells and whistles of Carbonite, iBackup, etc. While Dropbox has a lot more features lately, it's still major function is to allow computers to connect using Dropbox.
Crashplan is in the clouds and backs up your data automatically. You can access it from other PCs, but it doesn't automatically push the data to the other dropbox.
The other thing about Dropbox, which I use sometimes for file sharing (unless it has changed) is that once you upload a document, it is there forever. You can delete it, but it is not truly deleted. Tech support has to delete it. That stopped me from using it as I didn't want anyone seeing my files later.
