I have the good fortune to work for Sun this year as an intern in the some of their labs and part of my job is working with a lot with static sensitive devices from your simple PCI card or IDE disk up to System boards from prototype hardware running to Hundreds of thousands of pounds worth. We ALWAYS wear static straps, we have them attached to every single rack in the lab. Components don't generally fail immediately but a build up over time can often cause intermittent faults. So while you most likely will get away without using a static strap most of the time. For the people on this site who do a lot of fiddling with their hardware, its a good risk reducer, static straps cost very little and hardware can be expensive! and I'm sure we all know that the most annoying problem is an intermittent one!
I break stuff.