Using the PB as the main machine is a worthy idea that has no serious drawbacks unless you are doing something that involves high transfer speeds. The laptop drives are not as fast as regular drives. For increased storage, a Firewire drive would be suitable, along with an external DVD/CD-R/W, also Firewire.
I recently lost a 40G hd on my formerly friendly PC. I backed up with Nero, but have been unable to figure out how to replace the info...but that's another story.
I have a Powerbook 17 which has converted me to the, IMHO, superior OS and machines. I considered replacing the PC with a mac mini, since I have a good keyboard/mouse. Now I am wondering why I cannot use my PB as my main unit. I have a 320G Western Digital desktop hd, ready to go.
I would like opinions as to the feasibility of this plan.
TIA,
Ralphie Boy

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic