I used to have my PowerBook G4/400 w/Toshiba drive. It's not that bad. I went to xbench.com and checked out those new 1Ghz iMac. I clicked on 10 of them and they were all using Seagate drive (80GB ST380023A to be exact).
On my new dual 1.25Ghz PowerMac, it comes with a Seagate drive as well. (80GB ST380024A) While reading, it is noiser than my other hard drives inside the PowerMac; Maxtor 60GB 5T060H6 and WesternDigital 120GB 8MB WD1200JB-00CRA1.