you will always run out of hard drive space, eventually. laws of physics

seriously, anyone who does video editing (or wants to store dozens of movies) should get an external firewire drive for that purpose. video editing on system drive is just plain stupid.
that said, i ordered my albook with a 7200rpm 60GB hard drive and that's a very good backup when i don't have that external drive at hand and really have to do some work. partitioned for performance, leaving system on its own partition, i don't even have to worry about defragmentation anymore. if my /Users partition becomes too slow, i just copy it to the external and back

system will live happily ever after when nothing touches the system partition but the system itself.
(if anyone is interested, yes, you can mount another partition to any directory whatsoever. the config file controlling this is /etc/fstab which has to be edited with root account and i'd suggest you do this only if you don't mind the possibility of having to fix typos in single-user command-line mode. i have found it best to have a 15GB system partition followed by 25GB users partition, leaving rest (about 15GB too) for storage partition (mounted to /Users/Shared) where i have my itunes library. the reason for this: hard drive is faster on the beginning because of the laws of physics. by doing this kind of partitioning, i'm forcing system to stay in the fastest area and also forcing music library to stay in the slowest area. this will also reduce seek times greatly. and, should i wipe the system clean, i wouldn't have to worry about user data at all - just install the system and modify the /etc/fstab file again...)