Villain limp, 4-bets preflop. What the hell do I do?

[SuperUberBob]

Button is LAG preflop, but predictable postflop. No reads on MP.

PokerStars 0.50/1.00 Hold'em (5 handed) Poker Stars Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Preflop: Hero is SB with A[img]/images/graemlins/diamond.gif[/img], Q[img]/images/graemlins/club.gif[/img].
<font color="#666666">1 fold</font>, MP calls, <font color="#CC3333">Button raises</font>, <font color="#CC3333">Hero 3-bets</font>, <font color="#666666">1 fold</font>, <font color="#CC3333">MP caps</font>, Button calls, Hero calls.

Flop: (13 SB) 5[img]/images/graemlins/club.gif[/img], 5[img]/images/graemlins/spade.gif[/img], Q[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">Hero bets</font>, <font color="#CC3333">MP raises</font>, Button folds, Hero calls.

Turn: (8.50 BB) 7[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">MP bets</font>, Hero calls.

River: (10.50 BB) T[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">MP bets</font>, Hero calls.

Final Pot: 12.50 BB

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I thought the limp/cap was so freaking weird. I didn't know whether he was really weak (small ace, small pair). Or really strong (QQ+). So, I just called down.

What do people regularly limp/cap with preflop?