The servers are overloaded probably we just need to relax.
As with everything in life - (sorry for being philosophical) - when should one start to complain or question if something works?
Is there a set time, is it circumstantial?
The release date was set to the 17th of May - with Steam saying absolutely nothing about timezones or whatnot. The ideal case would be to release it at 1200 GMT, as nearly the entire world would be on the same date at that point.
Even if the release date was met in some parts of the world - several factors cause a feeling that Steam haven't really done their job well; the many hours after the XBLA release, the fact that they've had the files (they should be prepared to release it) and so forth.
Since distribution is their sole job; if/when they fail at it, complaints are in order.
Comparison: if a coffee machine couldn't make coffee - wouldn't you complain?
But if a multi-kitchen-tool couldn't make coffee (but still loads of other things), the problem seems smaller, doesn't it?
Again; a bit philosophical, but the nature of the "issue" and how Valve/Steam are handling their job, their customers and their distribution system... warrants a few questions, at least.