I think the intel architecture is a big help for the macs and that's for sure.
People who would never buy a mac before due to it being limited to... just a mac and it's associated software, will now buy a mac because it looks nice/has the apple brand look and feel and they can run their windows stuff on it too!
With dual boot they can obviously keep their known windows, and then explore into the Mac OS as well. Shrewd idea - especially if it can be found to be better
People get to try without risk, they can still run windows... and use the computer, but maybe they'll be converted to a mac in the long run
I personally don't give a monkeys about either - they're both big corps with a huge marketing strat and plenty of emphasis upon how things look above all else (as people are easily impressed!).
The good thing is they're breeding competition. Without opposition, what sort of OS would we have? They're both trying to innovate in different ways (or similar) to make sure they're the most attractive choice. Surely this is good for the consumer
I do sometimes just wish they'd both grow up and stop pointing fingers at each other and laughing / whining - reminds me of a playground :/