It's good to test and see if the guy will raise if you limp the SB.
If he only does it once every 4-5 times, you know he's probably playing too tight.
Most people lose patience in heads up, so if it goes on for more then about 10 minutes and you keep playing a good game they will make their mistake.
I agree with this - keep the agg up and usually people will get sick of it and push garbage. I had a a guy out chipped about 2/1 last night going to HU in a 105 Turbo on Stars, blinds 100/200 25. I got it to about 3/1 without ever showing a hand down, finally I raise from button with KJo, he moves in and shows me K6o.