I <heart> Adblock!
As a long time Firefox and Adblock user on various platforms, I never cease to be amazed at just how messy most webpages are when viewed with their ads intact.
Usually this is when I'm fixing someone elses IE only PC, which is often closely followed by a Firefox download, a quick Adblock and a cry of "Wow" from the PC owner.
Don't get me wrong, free websites are good, and for that there is obviously a price to be paid somehow, but does that mean I have to try and read a review in a 300 pixel wide window surrounded by bouncing ducks and other annoying animations? I'm there to read the review, not suffer an epileptic fit! If I didn't have Adblock, I'd be off of that site as quick as I could press backspace.
I know I'm going to sound just like my father here (not that he knows how to use a mouse), but in the good old days you might have the occasional letterbox animated gif at the top or bottom of the screen, but since the spread of the flash infection and syndication style sheets, the whole standard advert size and placement has gone out of the window, now you have squares and rectangles of every size all over the page. You even get adverts that appear over the text you are trying to read and get in the way! Possibly the most annoying ones being those automatic text sensing ones, which initially look like they might show a dictionary definition of a word, but actually just send you off to a back alley version of froogle!
One day when you're really bored, load up a page with, and without the ads (don't forget to flush the cache). Have a look at the bandwidth you use for each. Ads are sometimes over 80% of the total page download size! With some of the cut price ISPs having a 2gig a month limit, blocking this kind of bandwidth abuse starts to become a necessity!