I don`t know if any1s done any sort of poll in terms of what people just bought a ready built computer for.
I would put out there that prehaps a results may look something like:
1. Email
2. Internet (general)
3. Work/office related
....
4. Games
5. Music/media
Only reason I`d put Games down there is cos the majority or game players I feel wouldn`t want a pre-build so much. Similarly for coders, or coders who are worth their salt and don`t do it cos they have a piece of paper that says they can.
Anyways, the top 3 would give u a large market in 3 varieties only one of them being windows based.
It`s quite clever, I mean I can see my sister using a Mac, she just does theoretical top 3 there. Mother too. Nephews and nieces, I mean they have an Xbox or similar for gaming - perhaps the odd football management thing on a pc.