How do I stop blundering my queen? I have a particular bad habit when I play chess. I play reasonably well (at least by the standards of people I play with), and am quite careful with my pieces. But in about 80% of games I play, once I get into a good position - one or two pieces ahead and in control of most of the board - I nearly always move my queen to attack something and then lose her. This is usually due to an unappreciated threat (sometimes I've even seen the threat a turn or two before).

Is this a recognised problem for many players, or is it just me? If it is recognised, are there any recommended strategies to overcome it?
It's certainly not just you. While you describe a particular blind spot involving your queen, the more general phenomenon of throwing away sizable advantages is a very common one in chess, and it can be tough to kick. Here's a well-known saying that seems to be due to longtime U.S. champion Frank Marshall (and I'm paraphrasing):


  The hardest thing in chess is to win a won game.


I've read folks like Vladimir Kramnik echo this very point as well (as have thousands of others, I'm sure). So this kind of thing is something that affects the very best out there, not just you. There can be many reasons behind this kind of difficulty (e.g. stubborn, defiant resistance from the player on the losing end), but the primary factor that the winning player can remedy himself is simply to avoid "relaxing" too soon. After all, as your experiences show, even a huge material advantage can disappear if you let your guard down even a little bit and blunder away a queen.

Something I noticed long ago in my own games is that if I allow myself during the game even just to briefly imagine a future in which I've already won (e.g. hypothetical thoughts of who I'll be playing in the next round of a tournament once I've won), then things often become much harder the rest of the way, even if I immediately catch myself after the fact and refocus on the game. Is that real, or all in my head? It doesn't matter, because if it's in my head that's enough to affect my chess play.

Refusal to consider any game won until it's actually over, coupled with constant tactical vigilance, will go a long way to avoiding the pitfall you've described. Exactly how to arrange for that in your own head will vary from person to person, of course, but that general approach is important. Basically, what I'm saying here goes hand in hand with the nice point Wes makes in his answer (slow down, take a breather before moving); take every move in the game just as seriously as any other, whether it's the first move of the game, or you're up three pieces, because the cruel truth of chess is that an entire game's worth of brilliant moves can be ruined with a single bad one.