I have upgraded from 10.0 to 10.1 then to 2005LE and then to 2006 beta3. Never had a problem but over the years there are so many left over things remained I have 3 G more free space now after installing (cleanly) RC1, and the system is faster, don't know if they improved it or it's my doubled swap partition.
So I say if you wanna upgrade go for it, but a clean install is recommended every now and then.