Back in late 2007, I picked up a pair of HD3850's for a screaming deal to pair with my Q6600, but I primarily did not run them in Crossfire. I was playing EVE Online at the time and would often have two clients running on different screens, one screen per card. When using CF I had no complaints sans one: games needed to be run fullscreen in order for CF to function. I never noticed microstutter, and everything else I played, scaled.
In late 2008 I picked up an HD4870 at a great price to replace my 3850's (which I then sold and made a profit on) and found I actually lost performance in the games that I had bothered to use CF in, and also in EVE when running two clients. I threw a waterblock on my 4870 and appreciated the noise reduction though.
In early 2012 I paired the 4870 with my current 3570K.
In late 2012 I got a second HD4870 for $10 and ran them in CF for about 8 months. It was a pain having to switch from fullscreen-window to actual fullscreen, but Skyrim / Civ5 / GW2 all stayed at 60FPS+ where they had been in the 40's with a single card.
In mid 2013 I replaced my HD4870's with a 7850 which I got for $180 (and made about $100 in bitcoins on before losing interest) and sold the 4870's for $120. I lost performance in GW2 and Civ5 but was able to mod Skyrim due to the extra VRAM. It's also nice that I can again run my games windowed.
Around Christmas, I picked up a used 7850 for my wife's PC for $120. I figure when I get a new card, I'll CF the 7850's in her machine.
Overall, my experience with CF has been very positive. It gives value to cards that otherwise might be struggling to keep up with the latest games, and leaves a cheap upgrade path. Other than my wife's 7850, I think I've actually profited on my video card upgrades overall since 2007. Maybe right now is the time to sell the 7850's?