Its not just start up time (only relevant on reboot or VS crash), its the amount of time it takes for VS2010 to page back in after being idle for a few hours, its the amount of it takes to edit a file, the amount of time it takes for code completion to activate, the amount of time to build your project. I'm only comparing 2010 to 2008, Microsoft's biggest competitors are often its own older products!
We can speculate all we want on what the deal is with VS2010; I'm just happy 2012 seems faster.
That's a valid comparison - 2008 vs 2010 (versus the stupid VS6 comparison) - and one I agree with in many respects - especially UI responsiveness.
However, paging-in after idle-time is pretty similar, in my experience for both 2008 and 2010 (2008 fares worse for large solutions - especially if they have web projects in there). Build times are actually faster for VS 2010 (especially if you're on x64 - where it can use multiple cores). Symbol-loading when attaching to a process to debug is way faster for VS 2010 than in 2008. Detaching from a process also seems to have less negative consequences - VS 2008 just crashed in many cases.
However, VS 2010 is way too chatty in debug trace outputs. Also, slightly slower in parsing includes for IntelliSense after project load (not so during build though, funnily enough).
We can speculate all we want on what the deal is with VS2010; I'm just happy 2012 seems faster.