piowood doesn't know what he's talking about, not surprising with only 2 posts full of crap. Anyway, yes you can put 2, even up to 8 on one page (3 adsense blocks, 3 link units, 2 search boxes) each adsense unit can have a different adsense publisher id.
You can use 2 Accounts in same site but I'm not sure if you can use 2 ID's in same page. Better get clarify this from AdSense support.
check this out -Â http://code.google.com/apis/adsense/revenuesharing.html it is allowed but there are some condition need to be fulfill
multi adsense pub-id is allowed, bluearrow may have outdated information in his mind, when multi adsense pub-id on the same page was allowed only after asking adsense directly, now it's allowed without permission. The conditions lifeplayer is talking about is only for those who want to use the adsense sharing API, but that doesn't apply when you do adsense revenue sharing yourself like I do, with old adsense code format, just switching the pub-id in the code. on my sites I have often up to 3 different adsense pub-id, one for me, one for the author, one for the author's referrer.
multi adsense pub-id is allowed, but adsense with the same person name and address is still not allowed.
you can use more than one adsense account not only 2 accounts. and this is the basics of the adsense shared revenue system.
I think it is ok . If you have 2,3,4 .... Adsense account?.I'm sure if your site is not a web page revenue sharing adsense, you will soon be banned by adsense