Limping with AA/KK in EP: Always, sometimes, never?

[ticks]

Limped with KK in early position today,
with some success.
Now I dont want to be the victim of results oriented thinking,
so Id like to ask you how often do you do this with AA/KK?
What are the ideal conditons for limping?
When should you absolutely not do it?

Party Poker No-Limit Hold'em, $ BB (10 handed) converter

saw flop|<font color="#C00000">saw showdown</font>

UTG+1 ($40.83)
UTG+2 ($23.94)
MP1 ($26.7)
MP2 ($20.4)
MP3 ($11)
CO ($6.46)
Button ($5.32)
SB ($31.85)
<font color="#C00000">BB ($7)</font>
<font color="#C00000">Hero ($35.08)</font>

Preflop: Hero is UTG with K[img]/images/graemlins/heart.gif[/img], K[img]/images/graemlins/club.gif[/img]. SB posts a blind of $0.1.
Hero calls $0.25, UTG+1 calls $0.25, <font color="#666666">6 folds</font>, SB (poster) completes, BB checks.

Flop: ($1) 3[img]/images/graemlins/spade.gif[/img], 5[img]/images/graemlins/diamond.gif[/img], K[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, <font color="#CC3333">BB bets $0.5</font>, Hero calls $0.50, UTG+1 folds, SB folds.

Turn: ($2) 2[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
BB checks, <font color="#CC3333">Hero bets $1</font>, <font color="#CC3333">BB raises to $2</font>, <font color="#CC3333">Hero raises to $6.25</font>, BB calls $4.25 (All-In).

River: ($14.50) 4[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players, 1 all-in)</font>

Final Pot: $14.50

Results in white below: <font color="#FFFFFF">
BB has 5s Ks (two pair, kings and fives).
Hero has Kh Kc (three of a kind, kings).
Outcome: Hero wins $14.50. </font>