hi all, i havnt done a post in a while, but here is the question.in the diagram below, would Bxb3 be a bad move?

No, I don't think it would be a bad move. You would give your opponent doubled pawns and you wouldn't lose a tempo. On the other hand, you would be trading off your good bishop. Your other option Bc4 might be a bit better.

No, it's fine - it's much better than the alternative  ...Bxb3 weakens White's pawn structure but gives him the Bishop-pair, but you have to make a choice.  ...Bc4 trades Bishops instead, but you don't get to mess up the pawns, so White's space advantage means more.

After ...Bxb3 axb3 Nc5  Bf3 Qb6 Black is actually getting some initiative, too, so it's actually a pretty good move.

With Black to move, I'd play Bxb3 in a heartbeat. The white squared bishop doesn't have much of a future, so the question is really whether you want your rook on c4 or not. The c-file is half open, but the rook doesn't have much scope. You could plan an exchange sac for the c3 knight, but with white castled kingside this plan doesn't initially appear promising. To do the position justice, I'd have to analyze the variations for the rook following Bc4, BxB, RxB, but my initial impression is that you'll have to move the rook back to c8, in which case you have lost a tempo or two vs the simple Bxb3

No, imo Bxb3 is a mistake. This kind of "position" usually can be achieved from Classical Sicilian (my old vafourite Sicilian variation). This is what you should know about this position:

(1) Like in any other Sicilian variations, Black's weak d6 pawn is a big problem. Black should always find a way to advance the d-pawn. In this position Black has a plan to advance d6-d5 and Black strong control over the open c-file will make d5 possible sooner or later.

(2) The strong control over the open c-file is the key point in how Black will takeover the initiative and advantage from White. Black should strengthen the power of the c-file dominancy, e.g. by not letting it opened also for White, and by positioning the heavy pieces, especially queen and rooks on it. Black has also an option to sacrifice a rook for a knight on c6 to destroy queenside pawn structure a-la Sicilian Dragon. This may benefit Black in the pawn endgame.

(3) Black "key" strategy is to advance and exchange pieces through the open c-file and win the endgame (that's why I love this structure). Do not give White tempo to counter attack on the kingside (with its pawn storm)

Now after knowing the strategy to play this structure, I think it is clear that Bxb3 is a mistake. Here is why:

If Black should take over the initiative, he should release himself from d6 weak pawn problem. d6-pawn should be advanced and be exchanged with White's e4-pawn (exd5). If Black take the knight on b3 White surely will take the bishop with c2-pawn (cxb3). With pawns at d5 and b3, White may well put his bishop at c4 to make a strong chain, blocking Black open c-file, thus dismiss Black's counter attack. With no counter attack, White will have all the tempo to utilize his space advantage to prepare an attack (like in any Sicilian games, without counter attack Black is losing). If Black tries to capture the c4-bishop with his knight, White's queenside pawns are reconnected and will win the endgame.

I'm not really expert enough in the ...e5 structures, but while ...Bxb3 superficially looks good, I think it's important to look at the d5 square. ...Bxb3 removes one defender from the d5 square and does not remove an attacker. Given Black's bishop is being pushed away by f5, it makes some sense to play ...Bc4 to exchange a defender of the d5 square for a potential attacker of the d5 square (the e2 bishop).

 yusuf prasojo: excellent explanation of the theory of this position. Although I'm playing the sicilian a lot now, I've only played it since May 2009 and am still learning theory. Are there any books on the sicilian you'd recommend?

zugz: yes, I have answered this thru our private messages, but in case anybody else waiting for the answer, then I will answer here that I don't read opening books LOL.

It's strange how many (novice) players are after opening books, and how many opening books have been written. I'm not accusing of any conspiracy here. But then, if there is a part in chess where you can keep the information as a secret, it's the opening part! Do you think those masters will happily share their opening secret to their opponents? I don't think so.