Targeted Adverts on TV

Not really a new idea, clearly, but.... why o why aren't adverts on TV targeted?

It could be really simple, something like letting the viewer skip the advert (which starts another ad) and then recording the time of/type/style/genre of the advert skipped (or record the ones not skipped, either way will do). Then target the future adverts based on the recorded information.

The advert time slot remains fixed just the adverts vary. I guess it would mean the broadcaster would have to broadcast say 30 or so adverts (to be selected from) where normally there would be 5 or 6, and somehow monitor how many people watched each advert.

I realise this doesn't fit at all with how advert slots are sold/bought but surely that targeted advert is worth a mint to the advertiser. Also the broadcast/receiver technology is nowhere near, but how about on demand services skyPlayer, iTVplayer, Hulu etc, that seems like it could work by pulling the appropriate advert for the user into the video stream (pretty much how adverts work on web pages)

Anyway I think it would be great if the adverts on Tele were targeted to me, I'd probably even enjoy them more than the trash TV I watch.