I only use channels. However I do create ar least 4 adsense ads for each blog. Normally I name them after their sizes and where they are. For instance I have myblog-wideleft, myblog-largetop, myblog-largebottom and myblog-topwide. That info tells me which blog and which position is working best.
On my 3 coulumn blogs I put no adsense on the right at all. Worst ctr of all possible positions for me.
I start out with the widest on the very top, the 160x600 on the left bottom and then a large box on the bottom left of each page. Of those three the one to likely have the worst ctr will be the wide top. If that turns out to be the case I'll get rid of it and ad a large box at the top left of the page.
That's all for my pages. Posts get a different scheme because I use adsense injection plugin. I set it for the big box and left side.
You are right that it doesn't give me page info for ctr or any other stats but it does give me the info I need for each placement.
I'd much rather have the url stats but I just don't have the time to set up all of that for 30 plus blogs.