@Greg818: You're playing with some poor people if they think your cheating by cloaking, haha.
Plus most of the time the action is pretty packed up, so you don't really have time to stab and disappear, there's always someone or something nearby to kill your buzz.
Depends on the map, honestly. On a payload map you have a lot more set up time (and room) then on an arena map, and you can't really take the same time on a CTF map as you would on a attack/defend or control point map. It's all very situational; if you notice a route or pattern in the movements of the other team, it's worth it to set up and wait.
Next time I catch you on the same server, I'll do my best to put on a show (no guarantees! :D).