One massively compulsive game playable within another massively compulsive game? Why, that's like mixing Pringles with heroin. Yes, an official (from Popcap's end, at least) Peggle plugin has been released for World of Warcraft. Which is a) terrifying b) exciting and c) supports the viewpoint that MMOs are not merely a genre anymore - they're a platform all of their own these days.
The obvious response is "if you're bored enough in WoW to want to go play Peggle instead, you should probably just stop playing WoW." Which may be true, but it's not that simple - the WoW devout like to live in WoW - it's their internet. So this is a joyous thing - they don't have to leave Azeroth if they want to play something else, plus it's something to help while away those long minutes waiting for everyone to gather at the raid entrance or to cling to sanity during those oh-so-tedious cross-continental flights.
Sounds like Popcap have gone to some lengths to ensure WoWPeggle isn't some weirdly compartmetalised hoojum of its own either - it can be used to settle loot rolls, there's a versus mode, and there are customisable leaderboards (e.g. to create a ladder for your guild only). There's even a special Peggle talent tree, for heaven's sake. Aaargh...so...meta...hurts...brain.
Yes, this does signal The End Times. But it's Peggle! Inside World of Warcraft! Also, free and available already. There's also a similar Bejewelled plugin, which has been around for a while now - but, y'know, boring.