Speed.
But, yeah, I love my Pismo too. I bought it the day it was announced, back in 2000. The screen is not as bright as it once was and the hard drive is beginning to fail (the stock 12 GB hard drive it came with). The original battery is dead and the yo-yo power adapter is faulty. However, of note, the thing ran virtually continuously for several years...I was using it to run seti@home when it wasn't doing my "work." The only problem I ever had with it was with the sound board/power board (why those were engineered to be on one board, I'll never know)...but that was my fault, anyway. I shorted that board out due to me stupidly sticking a paper clip in there to try and hold an audio RCA cord which I had also stupidly broken a few weeks earlier. Anyway, my Pismo was a workhorse for me. I used heavily until I bought a Core Duo iMac in January. Once I replace the hard drive, I'm going to use it as a legacy system. I still have plenty of OS applications and games that I want to still play/use.