Followup on /home partition query

[alex]

I have Windows XP and 8 Linux systems but I'm thinking of using ubuntu
as my primary operating system. What would be a good size for a
separate /home partition for use with a 3 or 4 GB ubuntu root? 

Would there be a problem if that /home partition was also shared
with other Linux systems? (They're all ext3)  I currently have a single
swap partition that is shared by all my Linuxes--no problem.

alex, the OF