Commentary here: http://www.cnn.com/2009/HEALTH/06/26/hiv.test.day/index.html
The article sums it up really, really well but I'll put it here anyway: if you are sexually active, you should know your HIV status with certainty. And no, I don't mean, "Well, I donated blood four years ago and they didn't call me back so I must not have it, right?" There are clinics where you can get discounted and free testing. There are resources. Tests are anonymous, or you can do them through your GP if you're more comfortable.
Sure, people might look at you funny if you're low risk, but it's not their health, and it's not their loved ones. One in five infected people don't know they're infected. The estimated number of people who have aids is 1 million, which means 20,000 people are walking around with no idea. If your girlfriend or boyfriend is one of them, you have no way of knowing; HIV can have an incubation period of years
. According to the CDC, over 50,000 people in a year become infected - and 10,000 of them don't know. In the grand scheme of things, that's not a large number, but remember that it only takes one of them to make you a statistic for the rest of your life. There is no cure for HIV
So do it. Take some time. Get tested. For your peace of mind.
Oh, and donate blood more than once every four years, while you're at it. >.>