I tried the "shuttered glasses" type a few years ago (can't remember the brand name offhand)... it had a certain "neato" value, but it wore off quickly, and I never used it when flying online. In order to split the screen into left and right pieces, each half gets degraded... both in framerate and in intensity... so overall it looked darker and stuttery.
The only thing it really worked well on was looking inside the cockpit, up close... anything outside the cockpit may as well have been at infinite convergence anyway, so the 3-D effect would not help at all with any kind of external situational awareness.
So it's sorta cool, but not worth the money.
What IS worthwhile, if you're going to keep playing AH, is TrackIR. I highly recommend it, and I think it gives a better "3-D" feeling on a computer than true stereoscopic vision does, and it does not degrade your video image at all.