A less-than-optimal experience saving files online was one of my principal criticisms of Office 2010. Microsoft has acknowledged the issue and promises a fix for it soon.
Saving stuff online shouldn't be that difficult in 2010, but the implementation in Office 2010 is poor, often failing to work and taking an inordinate amount of time to save (and producing application-wide 'Not responding' errors while doing so). At the official Office 2010 launch, I mentioned this to the resident techies, who have since responded with news that it'll get fixed eventually:
The performance issue you are experiencing when Saving to Web from Office 2010 is known. It has to do with how the Windows File Save dialog communicates with the SkyDrive server. The Office team are aware of this issue and have a conversation going with the Windows team to build a case to get a fix for the scenario. The Windows team will triage and prioritise this issue and hopefully get a fix out soon.
It's still an odds thing not to have noticed earlier, but at least relief might be in sight.