When/Why does black do it? What kind of strategies should both sides adopt in such games? What kinds of games does it give rise to (i.e. positional or tactical)? Which players are well known practitioners of such a setup as black?
I found that the ECO B96 and B99 Sicilians include a line where Black castles long:
[fen ""] 1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bg5 e6 7. f4 Be7 8. Qf3 Qc7 9. O-O-O Nbd7 10. Bd3 b5 11. Rhe1 Bb7 12. Qg3 O-O-O
This is not a popular move, and probably not Black's best move.
Here are 3 Master games. Black fares poorly, earning 1/2 out of 3.
Spassky v Fischer, 1972. Fischer barely saves a dead lost position by finding a draw by repetition.
[fen ""] 1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bg5 e6 7. f4 Be7 8. Qf3 Qc7 9. O-O-O Nbd7 10. Bd3 b5 11. Rhe1 Bb7 12. Qg3 O-O-O 13. Bxf6 Nxf6 14. Qxg7 Rdf8 15. Qg3 b4 16. Na4 Rhg8 17. Qf2 Nd7 18. Kb1 Kb8 19. c3 Nc5 20. Bc2 bxc3 21. Nxc3 Bf6 22. g3 h5 23. e5 dxe5 24. fxe5 Bh8 25. Nf3 Rd8 26. Rxd8+ Rxd8 27. Ng5 Bxe5 28. Qxf7 Rd7 29. Qxh5 Bxc3 30. bxc3 Qb6+ 31. Kc1 Qa5 32. Qh8+ Ka7 33. a4 Nd3+ 34. Bxd3 Rxd3 35. Kc2 Rd5 36. Re4 Rd8 37. Qg7 Qf5 38. Kb3 Qd5+ 39. Ka3 Qd2 40. Rb4 Qc1+ 41. Rb2 Qa1+ 42. Ra2 Qc1+ 43. Rb2 Qa1+ 1/2-1/2
Pilgaard v Herrera, 2002 (white wins, the score isn't showing up)
[fen ""] 1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bg5 e6 7. f4 Qc7 8. Qf3 Nbd7 9. O-O-O b5 10. Bd3 Bb7 11. Rhe1 Be7 12. Qg3 O-O-O 13. Bxf6 Nxf6 14. Qxg7 Rdf8 15. Qg3 b4 16. Nb1 Qa5 17. Nb3 Qxa2 18. Qe3 Kb8 19. Qb6 Nd7 20. Qxb4 Nc5 21. Nc3 Nxb3+ 22. cxb3 Rc8 23. Bc4 1-0
Parimarjan v Krishnan, 2011
[fen ""] 1. e4 c5 2. Nf3 d6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 a6 6. Bg5 e6 7. f4 Nbd7 8. Qf3 Qc7 9. O-O-O b5 10. Bd3 Bb7 11. Rhe1 Be7 12. Qg3 O-O-O 13. Bxb5 axb5 14. Ndxb5 Qb6 15. e5 Nc5 16. exf6 gxf6 17. Bh4 Rhg8 18. Qh3 Bxg2 19. Qe3 Bc6 20. Nd4 Bb7 21. Nf5 Bf8 22. Ng3 Rg6 23. Nge4 d5 24. Bxf6 Rxf6 25. Nxf6 d4 26. Qe5 dxc3 27. Rxd8+ Qxd8 28. Qxc3 Qc7 29. Nxh7 Qxf4+ 30. Kb1 Be7 31. b4 Be4 32. Ng5 Bxg5 33. Qxc5+ Kd7 34. h4 Bf6 35. h5 Bd5 36. Qb5+ Kd8 37. Qa5+ Kc8 38. Qc5+ Kd7 39. h6 Bd4 40. Qb5+ Kc7 41. Rf1 Qxh6 42. Rxf7+ Kd6 43. Qb8+ 1-0
This game is interesting because, statistically,
13. Bxb5 seems to be a refutation of
12. ... O-O-O, with White winning 2 times as frequently as Black. The percentage of draws is low, so if you play this you better be ready!
13. e5 may be an error with Black winning 2.5 out of the 3 games in the database. There are no master games with this continuation.
Look how Black's
g7 pawn falls in the first 2 games...
Black castling long in the Sicilian is a rare thing indeed. I can think of a few reasons:
Black castling long is very rare in chess in general, only a few slow going openings (Caro-Kann, Scandinavian) feature it in general. It takes longer to prepare for long castling than for short castling, the king is less safe on c8 than on g8, white moves first so it's even riskier for black than for white.
In the Sicilian, white generally gets quick development and an attack so it should be even more dangerous.
Black has moved 1...c5, making the queenside less fit as a home for a king.
Besides, one of the ideas of the Sicilian is to play along that c-file with a rook on c8, doesn't combine well with castling long.
So in general black only goes queenside if white has a full-force attack on the kingside and the center, and there is basically nowhere else to go.
I can think of one exception right now in the c3-Sicilian, where the queens are off the board and black can castle with check:
[FEN ""] 1.e4 c5 2.c3 d5 3.exd5 Qxd5 4.d4 Nc6 5.Nf3 Bg4 6.Na3 e5!? 7.dxe5 Qxd1+ 8.Kxd1 O-O-O+ *
and lines similar to that.
Normally, you don't want to castle "long" in the Sicilian because of the missing c pawn, which can make the king very vulnerable to attack.
An exception to this rule is when White has "wasted" a lot of moves on the king side, usually through a pawn "storm" before you castled. This would have given you time to get a center counterattack going. Then, castling long puts a rook on the d file which may be the coup de grace to White's center. More to the point, you will be able to "snipe" at White's exposed kingside pawns, and ultimately his king (which will probably be there, or in the center), without danger to your own king.