I run AdBlock Plus when I am using Firefox (95% of the time). I have quite a few sites "whitelisted" so their ads appear. If I find myself going to a site all the time and using their bandwidth and knowledge, then they deserve some revenue. On the other hand, I'd rather see a site ad-free if its an "unknown" site.
I had a site that was moderately successful for a time. At its peak, it was averaging over 1000 "unique visitors" a day. I put up ads to defray the cost of running the site. The rest, I promised, would go to a charity closely related to the site's content. After running the ads for 3 months, I had to shut down the site. One of the many reasons was that I was paying more than the ads were bringing in. When looking through logs, I saw that most ads were being blocked, so I wasn't even getting the fractions of a cent for impressions much less any actual click-throughs. Even my regulars were blocking the ads, which were the only source of income the site had.
As for ad supported software: as long as the ads only appear when I am using the particular software, I have no problem. If I recall, Eudora used to have an ad-supported version of their email client that I used exclusively throughout college. If the program installs some other kind of ad-generating software on my computer, however, it's not ok and the software goes in the trash.