I think it depends on what you're seeking to do with it. If you just want to "check it out" then you could select 10GB for OtherOS but if you plan to dump some serious large PS3 games (and you have a 60GB drive) you can select 10GB for the PS3 instead... unless you plan to dump to an external drive.
Me personally- I don't 'PLAY' many PS3 games (not enough free time) and I actually use the PS3 more for tinkering, dumping, etc so I selected the 10GB to be allocated to my PS3 out of my 60GB HDD. I also only have a 128MB jumpdrive (with the otheros.bld files on it) and my external 40GB HDD is occupied so I dump to my PS3 internal drive directly and then transfer the files from it to my PC.