Never BOUGHT the same one again, but I do have/had several duplicates. I bought one NIB AT101W, but I got another two for free later (along with a AT101), I bought a NIB Model M but got an older one this Thursday, I have two G80-3000s, one with black and one with blue switches, both for free, and I got three Acer 6312-TWs for free.
I'd never BUY a duplicate though. Most of my duplicates I disassembled for parts, in fact.