Carrara can take a little time when it closes depending on how much there is in the page file, as well as some other factors.  I had mine take 15 minutes once because it was a very complex file.

Quote - I have next to no crashes with Carrara. Compared to Poser, Carrara is mega-stable.
The only problem I have with C6 is after I have had it open for several hours, it refuses to close.
I can close the current file, but the program will not stop. I have to shut down with the task manager.