I'll add my 2c - because I did a clean reinstall of Lion earlier this year.... took probably an afternoon and an evening to do 99% of it - I found it well worth it to be honest, certainly fixed an irritating bug I couldn't solve otherwise (external drives losing contact with Finder)....
I didn't find it that much of a chore, just a good spring clean out really! After 3 or 4 laptop purchases and migration assistants a lot of detritus collects....