I downloaded SpeedFan and it reports that my CPU temperature peaks at about 73C which seems to be normal according to this chart (although the little flame icons in SpeedFan worry me).
However, is a CPU fan speed of 3590 RPM normal? The CPU fan reaches this speed after I e.g. open thunderbird, tweetdeck and a youtube video in firefox. At this speed the fan spins so vigorously that I can feel a light vibration in the table above the computer, and it makes a high pitch drone/whine like an airplane taking off. Is my fan broken or is this speed much too high for a CPU fan?
73 degrees is a little high if you ask me. The RPM of your fan is determined by a host of things but ~4000 is fine I tend to like slower fans that move more air because they are quieter.
If the noise is bothering you buy a large fan/heatsink for $30-40 and replace it
EDIT: After seeing the pics... That looks like a stock CPU fan, I'd replace it with something quieter, it will bring the temp on your CPU down and be much quieter. When you pick something make sure it's going to fit. You don't have a whole lot of space between the CPU and the RAM
Yes, 3500~4000 is normal (possibly even on the low side). By the look of the photo, though, you have a stock heatsink and fan assembly. I would recommend buying something like an Arctic or a Zalman cooler assembly.
Do check the internal dimensions of your case, though, as some of these more expensive coolers can be pretty sizeable.
The RPM is normal I would say. Temperature is a bit high. Would be wise to maybe change the Fan for a better one. Or more importantly make sure that you have some circulation through your computer case.
My computer was very unstable, although in my case it was the PSU that was getting too warm. Anyways, it was fixed by getting a new case that allowed for some fans to be put on the front, back and side. I had one in the front and on the side blowing in. And one on the back in addition to the PSU to suck air out. Helped a lot.