It's pretty frustrating.  Whenever there is a contest I want to enter, I end up having to remove half of the elements that I wanted to include so Carrara won't bomb out with those infuriating Memory Allocation Errors.  It may be one of the lower cost 3D modeling packages, but it is still a pretty hefty chunk of change for the amount of frustration you have to put up with.  If there wasn't the great online help resources like Renderosity's forums, I would probably be in jail for shooting my computer by now.  Either that or bald from ripping my hair out.  I have no idea how folks manage to get their machines to do some of the more advanced renders I see here in the galleries.  I am on such a tight budget that I can't even afford shader ops and anything goos, so I have to try and do things like aging and dirt/rust in other creative ways...  And sometimes; Carrara just does not want to cooperate.