I hadn't realized before fooling around on ebook comparison site Leatherbound.me that the Nook and iBook stores had such a rubbish selection of books. It wasn't until I typed in "Twilight" that I actually found something available on all stores.
Not only could Leatherbound.me help owners of different ereaders decide which store to download from (err, all one of you out there), but it could actually help decide which ereader to buy. Most potential buyers should have some idea of the books they'd like to download first, so knowing which platforms they're on will be the deciding factor. From my brief play with the site, it's obviously the Kindle, but I'm sure you've got better taste than me...[Leatherbound.me via CrunchGear]