I usually don’t like seeing ads when I’m browsing the web, but I generally don’t block them because my brain does a good enough job of tuning them out and I accept them as a necessary evil because I understand that publishers (including me) need to get paid, and an advertising supported business model can work.
I find it harder to ignore the ads that force themselves over the content I’m trying to look at, but I don’t generally block those either. Animated gif ads flirt with my attention, but I don’t block them either.
I do block flash ads on websites I visit regularly using Ad Block Plus, and anyone else who serves flash ads from the same ad networks are collateral damage. I do it because I keep a lot of tabs open and all those flash scripts end up using a significant amount of CPU, which slows everything else down and drains my laptop battery.