when to trade queens?

Would it be a good basic princple when playing to alwayss exchange queens when you can go up a minor piece on the exchange??

Making this exchange leaves you a piece up, so of course it's a good idea.

I'd second this (the exception would be if you could force mate by another move).

In general I'd say, go for exchanges (including the queen) if you have material or other advantage (simplify the position). If you are in disadvantage, avoid exchanges since they help your opponent. (Again, there are exceptions - if you can exchange a piece that threatens mate, away with it)

I usually make an exception of those rules-of-thumb when playing someone much stronger (like a master in a simul) when I know I'll certainly lose and could resign even after the first move if it wasn't for the fun. In this type of situation I always try to go for a Q exchange b/c as long as the Q is on the board, I'm certain to run into some mating tactic. With Qs exchanged there are chances I'll make it into some type of endgame and say to myself "at least I battled him for one hour / 30 moves / whatever" :)

Unless it gives my opponent an overwhelming attack I'll always trade queens to win a piece. I'll usually trade queens to gain a pawn. Heck, I'm likely to trade queens if it only gives me a better position than my opponent.

Chess rule # umpteen: If it gives you an advantage, do it.

It's almost always a good idea to win a piece and if you can also exchange queens that's even better.

Does it ever slightly annoy you, when you're playing with someone close to your rating especially (neither player has significant edge over other), when the line between the two opposing queens opens up for some reason, and your opponent swoops down and exchanges queens, for no other reason than to exchange them, i.e. no one gains anything from the trade? It seems like it's usually toward the start of the game, and the two pawns in front of the queens have been removed, exposing the queens to each other. Does this ever get on your nerves lol?

nope.  i will trade queens anytime it results in a better or equal position.  the queens are the strongest pieces, so i prefer to get them off the board so i don't have to worry about them. 

that's true, but at the same time it's somewhat harder to bring about checkmate without one's queen, depending on how even the rest of the game is material-wise.

I'll usually trade to prevent my opponent from castling.

This really depends on the kind of advantage you have. If you, for example, have a space advantage so that your opponent's pieces are in cramped position then you naturally want to avoid exchanges that would ease this cramped state.

exactly...oh, you meant that as a bad thing.  i mean it as it is harder for my opponent to checkmate me. 

That's a little bit of a disadvantage, sure, but once my opponent's Queen is gone, castling is usually no longer such a high priority for me.

Good point but I'd usually take that small advantage.

I know you should play the board but if I determine my opponent is a little over-reliant on his queen, I may try to force an exchange. Even knowing my opponent will be reluctant to exchange can be useful.

I guess the rationale could be to exchange a more active piece (or potentially more active) for a less active piece rather than just making him uncomfortable.

i usually trade queens early in the game.

its a part of my chess strategy. LOL

I know this thread is old, but wanted to add to it.  

I do this all the time.  It usually results in my opponent either having to move his King early in the game, leaving it in the center for attack (even without the Queens on the board, with all minor pieces and most of the Pawns/both Rooks, it's a bad thing to have your King so exposed), or them being forced to take with their Knight on the C file, or Bishop on the E file if they've developed it to there.  This gives me a tempo, lead in developmenet is the potential to gain more central control.  A general rule is to never be the one that opens up that file.  It's good strategy to force your opponent to make one of these backwards moves (or move their King), and should put you at a major advantage for the entire game.