If I understand it right, the ads are displayed initially and are still in the background when reader is on. If an ad is interesting enough, the user would still see and click it.
Well, Safari5 Reader's approach may make that feel less necessary - since one can easily click in and out of Reader-view.
And an advantage (as I test-drive it) is that turning the Reader-view on/off for a given article is almost instantaneous: whereas with Readability to move _out_ of Readability-View involves _reloading_ the entire page (which I find annoyingly slow on pages like TechCrunch, RWW, etc where there are tons of ads to be (re)loaded.
I think the Safari-Reader approach may increase time I spend with a full, ad-laden page open.
Because non-print versions kinda blow. Spanning a single article over 10 pages with a few dozen words per page just so you can get 10 times the ad impression is not acceptable.
