I meant to reply to this thread a Tuesday, but I wanted to think out my response and ended up getting distracted by work. The thread has grown beyond my meagre attention span's ability to sift through all of it since then, so apologies if some of this sounds repetitive.
Go for it Brett. Nobody here should resent the need to raise capital, which gives you the ability to hire (more) staff, invest in contract coders, and of course, reward yourself financially for the outrageously useful venue that you've provided to your users over the years.
I have absolutely zero doubt that there are hundreds of profitable webmasters out there who owe great debts to this site for the ideas and discussions that can be found here and nowhere else.
Go for it, but be very careful, and expect problems.
If you are going to keep a "walled garden" for supporters, then make sure that the supporters don't have to see ads. Ever. In any form.
Consider getting rid of the supporters "walled garden". Of course, you would first have to determine that the revenue lost from the supporters area was more than offset by advertising revenue. One of the things about WebmasterWorld that has annoyed me for some time is supporters section threads that get front-paged. There was a time when I was using this forum much more heavily than I am now (career has moved into a direction that makes this forum somewhat less relevant to me personally), but the front paging of supporters forum threads decided me against contributing. It seemed like a cheap baiting tactic, and got my hackles up. However, if you put advertising on the site, many people (myself included), would feel they would be "paying" for the content in the act of being subjected to advertising, and thereby a separate area for "contributors" might seem like you were pushing it.
Don't use a stock program like Adsense or any of the others. The crowd here is savvy enough that those types of programs will simply be looked past, if not actively blocked. AdBlock is a cornerstone of my web surfing experience. It makes otherwise atrocious sites tolerable (dead tree News publishers who have websites I'm thinking of you here), and I would argue that a high percentage of this crowd has some form of Ad Blocking technology built in that would filter out any of the stock advertising/affiliate programmes you could tap into.
Lead by example and build it out yourself, and with the help of some of the deep minds here. And then tell us how you did it. Seriously. There are many people here who would love to break out of the grip that the big affiliate programs have on their sites, who would relish the chance to explore building out their own, in house advertising program, if only they could see a winning example in action that demonstrated how to do it right. This place is, and always has been, about surviving and winning as an independent webmaster. Taking full control of the advertising revenue stream is a step towards greater independence that many here are afraid to take, because they have real world concerns (mortgages, families, employees), and the risks involved with taking advertising in house can be a little daunting.
Be careful how you combat ad blocking technology. Don't get into an arms race. You will lose. Technologically, there are far more people actively working on ways to get rid of advertising than you could ever hope to hire to work on the problem. Socially, in engaging in that battle, you would anger a huge segment of your users and just drive them away. Is it Ok to have a little nag message show up every now and then saying "Hey, I know your using AdBlock, could you disable it for this site? Throw me a bone, brotha..." or something along those lines? I'd say sure. I've seen those messages on other sites, and I've even clicked the option to disable ad blocking for those sites from time to time. Ask politely, and you never know, some people will probably play along.
If you decide to allow image based Ads, keep a firm editorial approval process on the types of ads you allow. Nothing "blinky" or moving, nothing garish or gaudy. Those ads have a place - they have a target audience. That place and that target audience are not here.
Make money. Live long and prosper WebmasterWorld - you've earned your rewards.