We've been backing up to the 'cloud' for a few years now, but the size of our databases are not so large as to cause a problem, I guess.
Or, since the backup company we've subscribed to uses the VSS shadow writer to capture disc-writes and sends those every 15 minutes.. maybe their's just not too much there to cause a bottleneck... I really have no idea exactly how much it sends through the pipe, but it's not noticable. And the test-restores work just fine.
Of course, we also back up db's nightly, and tranaction logs hourly (to a separate sever), and back up those backups to tape nightly, too.
I don't bother taking the local, physical backups off-site anymore since we have the copy 'out there'.. they're for my own comfort and convenience.
Just a cog in the wheel.