Carrara does have memory problems and they are a lot worse than V5I's, in my experience, although rather like the ones Vue 4 used to have.   With Vue 4, if a scene got complicated, it tended to be a toss-up:  do I save the scene and risk a crash that way, or do I invite Vue to give me a multi-fingered gesture by trying to render it?   I have had that same experience with Carrara 5, too, whereas V5I is much more reliable (again, in my experience - no doubt, different hardware configurations make a difference).   I have known V5I to fail to render something, but still leave me able to save an intact file and successfully render it later.   If Carrara fails, forget it.   It will come out with that cryptic message about line 42 (or is it 45?) and you can forget about saving the file.

And Phantast is right:  Carrara's modelling element may be a "nice-to-have" in a basically non-modelling application, but buying Carrara because it can model (to some extent) is like buying oranges for the sake of the pips.