If you look at the specs, the desktop drives usually can do 8ms seeks while laptop drives go only as fast as 10ms
Also
I did a benchmark a long time ago of my toshiba 5400rpm and it averaged 27MB/s or so
I've also seen other benchmarks for 7200rpm Hitachis that are around 33-34MB/s
Compare that to an average of 54MB/s for the latest generation of high density desktop PATA drives