My usual mistake

[Cerril]

MP2 is LA-A, everyone else is passive postflop, though to be honest I feel like this is less of a read-dependent hand

Party Poker 2/4 Hold'em (10 handed) converter (http://www.selachian.com/tools/bisonconverter/hhconverter.cgi)

Preflop: Cerril is MP1 with A/images/graemlins/diamond.gif, 3/images/graemlins/diamond.gif.
<font color="666666">[i]2 folds</font>, UTG+2 calls, Cerril calls, <font color="CC3333">MP2 raises</font>, CO calls, Button calls, <font color="666666">1 fold</font>, BB calls, UTG+2 calls, Cerril calls.

Flop: (12.50 SB) 3/images/graemlins/heart.gif, 5/images/graemlins/diamond.gif, 2/images/graemlins/diamond.gif <font color="blue">(7 players)</font>
BB checks, UTG+2 checks, <font color="CC3333">Cerril bets</font>, MP2 calls, CO calls, Button calls, BB folds, UTG+2 calls.

[i]I immediately thought 'checkraise' as soon as I hit the bet button. MP2 just calling was maybe lucky, maybe not, but was playing it safe here (since obviously the checkraise would be for value) the better way to go?

Turn: (8.75 BB) Q/images/graemlins/heart.gif <font color="blue">(6 players)</font>
UTG+2 checks, <font color="CC3333">Cerril bets</font>, <font color="CC3333">MP2 raises</font>, CO folds, Button folds, UTG+2 calls, Cerril calls.

Same question as the flop, though it may be even worse here since 12 of my outs will likely beat the entire field (while the other 5 aren't terrible), and there's no chance of winning it outright.

River: (14.75 BB) 4/images/graemlins/diamond.gif <font color="blue">(4 players)</font>
UTG+2 checks, <font color="CC3333">Cerril bets</font>, <font color="CC3333">MP2 raises</font>, UTG+2 calls, <font color="CC3333">Cerril 3-bets</font>, <font color="CC3333">MP2 caps</font>, UTG+2 calls, Cerril calls.

Final Pot: 26.75 BB
<font color="green">Main Pot: 26.75 BB, between MP2, MP3, UTG+2 and Cerril.</font>

Pokertracker lists my final hand as 'straight flush, two through five'... Wow! I wish I'd known I only needed four cards to win!

[Alobar]

I have no idea what LA-A means, but anyway...

this is the easiest flop checkraise ive seen in my life. by not doing it, you cost yourself a ton of bets.

everything else looks fine.

[Cerril]

(LA-A is bison autonote-code for LAG preflop-Ag post, those three/four-letter demarcations have helped the way I think about my opponents tremendously)
Yeah, though by asking precisely that I worried about baiting exactly the response I mostly wanted to confirm that it was indeed a boneheaded knee-jerk bet.

Turn bet not a problem?

[Alobar]

with the way you played the flop, the turn bet is standard. You'll likely get enough people to bet for value. If however you can assume that MP2 (due to your aggresive read of him) will bet this turn if you check to him, I go for the checkraise. There is still alot of people in this hand and you will likely get enough callers of his single bet, to raise for value. If there is a big doubt tho, I prolly just go ahead and bet.