Oh yeah, formatting the drive now would...well... not make any sense.
I personally have an 80GB SATA (as opposed to IDE) drive in my main machine - with a 20GB partition for the OS and software and 60GB for the rest of my stuff. Right now I have 11GB of my 20GB partition free..

That's amazing to me since I have so much software. I regularly back up the 60GB partition onto the 30GB and 40GB drives in my server (this way if my main drive fails completely, my last backup might only be missing a week's worth of data at worst). You see, 4_degree and I have 3 computers - one's his and the other two are mine - one of which acts as the server for the other two. It's an easy way to store mp3s and other files so they can be shared across my wireless network.
I see no real advantage to leaving additional space for the OS - actually I should think that would slow it down a bit, mostly because the more space the OS and software are spread across, the longer the drive's seek times to find the correct data. I mean we all know Windows is a resource hog - and just the fact alone that it uses a portion of your hard drive as virtual memory should prove that to you

. That may not entirely be correct - but hey.. it sounds right.
EDIT: Oh yeah, and if you're like me - running lots of intense apps at the same time (music, photoshop, etc, etc) you might keep an eye out for the new multicore procs coming out - I'm looking to upgrade to one next year sometime. That would help with multitasking.
