I have a 3D TV. Worth it? Meh.
They way I see it, the TVs currently on sale have 3D anyway and you don't wind up paying more to get it, so it's not a terrible investment.
How often do I use it? Rarely, but a good 3D movie or even some video games in 3D is a pretty sweet effect.
Be advised, there are two different kinds of 3D glasses, passive and active.
Passive are the ones used at the movie theatres (aka take them home and never buy them) and these just use two different lenses for prespective, while the Active are the ones that are heavy, battery powered and much more expensive. These are also more likely to give you a headache due to the lenses rapidly flickering to trick your eye to see two different things.
Do some research if you're seriously considering it, but it's nothing outstanding you need to go for. If you're going to get a TV and it has 3D, I suggest passive since it's cheaper and less painful. I was pretty pumped when I got it because I had Call of Duty, L.A. Noire, ESPN 3D and fios has a 3D special on video on demand with 6-12 movies free for 3 months, then the next few months they switch to new movies.
Keep in mind, if you're mounting your TV, 3D capabilities are best viewed straight on. Even if you're going to be on a couch and about a foot lower than the TV this could drastically effect the 3D effects, so try it out in store before you purchase.
Any other questions, please don't hesitate to ask.
Not that it really matters, but they do already have a 3D TV that does not require glasses. It's only available in Japan and it's something insane like $11,000 for a 12 inch screen.