I think the reason we haven’t seen this problem before is because our .Net apps have been a lot slower that Rails. Slow enough to keep this IE bug from showing up.
That is certainly something that I have seen before. The main problem is not the runtime performance, it is the initial performance. If I make a change to a page, I have to wait ~30 seconds for it to load. Contrast that with making a change to a MonoRail view, where a change in the view appears instantly. The problem is that changing the controller requires re-compilation, which has the same performance penalties.
This is something that kept me annoyed, but it is getting more so lately, because I can feel the difference between changing the view (brail, instant) and the controller (C#, ~30 seconds), where before anything that changed caused the same long delay.
As far as I can tell, this has to do with AppDomain load / unload, but I never really bothered to take a look. William was talking about this same problem a while ago. This may not affect the runtime production performance, but it plays hell with the developer's performance.