Hey, I recently bought last week a incase case for my MBP and I do got to say it works really well. It very nice and fit tight. It does add a bit of more weight to it but its very minimal and it does not bother me at all. I havent really noticed about dust collecting in since I recently bought it but I gave it a really good clean before put it on so I think its fine for a while. I do reccommend the case, oh and it doesnt really make a difference heat wise at the bottom. It actually feels a bit better.
hope that helps.