Home will be free but it will be a massive download unless they run in constant streaming type thing. Remember every1 has their own space nevermind themed rooms etc. all in HD. Most demos are around 1GB and thats normally only part of a mission. I think home will weigh in at around 5GB. Thats a lot of space unless you have the 80 or 160GB model.
I have put a 320gb hard drive in my ps3, so that won't be a problem for me!!