This means that dropbox no longer "syncs". It's just another harddrive in terms of how it works. Copies to and from just as quickly as your harddrive.
Heck, it seems like if you installed an application to your dropbox, and ran your computer off of an SSD, it seems like you could enjoy BETTER performance than if you had that program installed on a 7200rpm drive and ran it locally...
Can't wait to see what we end doing with 1GBit ubiquity!
[1] http://www.tomshardware.com/charts/3.5-hard-drive-charts-200...
Second, even if it were running the application from Dropbox's server(s) (it seems like that's what you mean?), it would still have to read from their servers - you can't magically eliminate a bottleneck just by moving it to a different physical computer; data still has to be read from disk.
Think about it; with that kind of a pipe, you could boot your desktop off of a drive in my datacenter, two cities away.