You know a file synching utility like Dropbox has gone horribly wrong when Mail in OS X downloading its latest messages and attachments looks like a speed demon by comparison! I shouldn't have to choose between getting an unedited file out of Mail to start working or waiting for my file synching utility to finish "starting" so I can get the copy I worked on.
I've been using the latest preview Dropbox for OS X builds for best OS X 10.8 compatibility. At the time of the writing, 1.5.47 is the latest and the performance hasn't been very good. In fact, I've seen this in many Dropbox builds at this point. I use Dropbox to keep a MacBook Pro and iMac in sync. The MBP is sleeping most of the time. When I need to get work done, I wake the MBP from slumber, then dutifully wait for Dropbox to pull down changes.
This cycle is one of the worst so far. 15 minutes for Dropbox to complete it's "starting…" phase, 5 minutes for "indexing" and finally around 20 minutes after waking from sleep, Dropbox is actually downloading files.
I know, everything is amazing and nobody is happy, but for a product whose sole reason to exist is file synching, bad performance can't be tolerated. Box.net is even worse, so not even an option.