7200RPM made a big difference in my lappy
When you run any sort of benchmark that combines all factors of pc performance the HD is only one part of that score. As others have mentioned it is big bottleneck. My personal experience is that the HD upgrade and bumping the RAM up by a Gig was the biggest bang for the buck to date.
I can't tell you how much snappier my lappy is now. I upgraded the HD to 7200 RPM and now my bootups in XP Pro are 17 seconds until I get my login screen on my corporate network and then only 18 seconds to login after that. That is excellent performance compared to my 45 seconds before just on the first phase of the bootup process.
My images take much less time to load in Photoshop and even editing them is faster due to the HD and of course more RAM. People now stop by my office and drool over my lappy!

I took my old HD and slapped it into an external USB 2.0 enclosure and now I have 120GB always at the ready. I use it mostly as a backup drive image so I can immediately recover my work if I have an issue.
Once the 100GB drives are available in 7200rpm I will upgrade and my current HD will become my backup and my other lappy will get the bigger drive. Trickledown upgrades at work!
