I did!
We did Dinner with an Imagineer in January 2004 (for my birthday). It was just me, my husband and an older couple who, from what I remember, had been given the dinner as a gift from their children. However, the dinner they were supposed to have was with an animator ... aaaand this was right after they canned all the animators in Florida. So they were a tad confused as to what the Imagineer did.
It was an
awesome experience. The food at the Brown Derby was to die for, and you're in this little side 'bamboo room'. They made customized menus for all of us (to take home), and we each got a commemorative plate that our Imagineer, Eric (I think? I'd need to look it up), signed and wrote a message on at the end.
I remember it being about ... 2 hours? long. I think. It was really obvious why or how he got picked to do these dinners, too. He was just ... ultimate personable Disney. Really nice, happy to answer any questions about what he did and his history with the company, etc etc. He was actually fairly new to Florida, coming from Glendale. He'd only been there a year or so, and his most recent project was Mission:Space (actually one of the 'post-ride' games.. the one where you hop around in the little suit and try to get your guy to safety or whatever).
It was kind of hilarious after a while because he was so new to Florida, he didn't know some of the answers to questions about WDW that the older couple was asking and, not being able to help myself, I started answering them. Which, thankfully, he was totally cool with.

Once he and the Brown Derby manager had worked out how many times I'd been to WDW, they started suggesting other attractions in the area that we might do, too, which I thought was really nice of them. (I think the end recommendation was Gatorland).
With regard to any fork stabbing - to be honest, we weren't asking any questions like "Why do things suck now?" and I suspect if we had been he would have tactfully Disney-answered us away from that topic. (I mean, he's being paid to do this, he's not on his own time; he couldn't even have the wine pairings for the courses). That said, he did make some comments that suggested to me that things were a little weird in Glendale as far as job security and how the place is run. When I mentioned that I'd wanted to be an Imagineer way back when, but that I was a meteorologist now and didn't see how it'd work out, he was talking about how all kinds of bizarre professions end up under the blanket of WDI (I think the specific example he gave was someone studying pest management, like they do at Epcot). That, and a few other things, sort of gave a vague image of a typical bloated corporate entity, rather than a hive of super-creative people.
It was fascinating, anyway. I'm not sure I would do it again because a) it's expensive and b) it was really a perfect evening as it was and I'm not sure, 4 years down the road, if we'd get someone so bright-eyed. That and I'd be more likely to get fork-stabbed nowadays.
Anyway ... I could ramble about this for some time (read: tl;dr). If anyone has any specific questions, fire away.