I think in many cases they're necessary. If it wasn't for ads there would only be 6 tv channels in this country. Most of the websites I frequent wouldn't exist because they wouldn't be able to afford to exist.
In many cases I think they're great, when they're inconspicuous and save me from having to pay.
The idea of paying to read a movie review or blog post just wouldn't work when people have a free option.
I do like sites like XKCD that make their money from selling things rather than adverts but in many cases that just wouldn't work.

Still, in many cases they could be more subtle but then would you notice them? I know I never click on adverts and block most of them out (particularly on sites where I'm familiar with the layout)

Adverts in things I have to pay for are annoying. I know it's how magazines make money but it's still annoying in 3D world when you get 30 pages of adverts (once there was a 21 page Dell advert....). Still, if it saves me money then it's fine in moderation, but maybe they should have to put on the front the percentage of adverts, so when you buy a thick magazine you know it's only thick because of adverts.

But my god, TV adverts in america are insane on some channels.