IR thermometers can be great tools. A couple of cautions:
1. All of them have a specific Field of View (FOV) which is basically an indication of their ability to resolve a target of a specific size. For basic maintenance equipment you should have an FOV of at least 45 to 1. This means at 45" you can measure a 1" target, at 90" a 2" target, etc. Many of the low cost units ($100) have only a 6 to 1 FOV; this means you'll have to get VERY close to measure anything.
2. The laser aiming device should define the target size rather than being a single point. Most fully featured systems ($400-800) have a rotating laser circle that really works nicely.
3. You will not be able to measure temperatures of shiney, metal surfaces (or even oxidized ones), due to the fact that they do not emitt energy efficiently. You'll get a temperature, but it will not be accurate. EVEN if the device has an emissivity correction feature (and many of the higher end systems do), expect huge inaccuracies on unpainted metals.
4. It is very difficult to "scan" a large area with a spot radiometer. If you are looking at a limited number of specific connections or pieces of equipment, then they can be useful. Good used infrared IMAGING systems can be had for $2000-5000 which will do a much better job of scanning large quantities of equipment. There are now a number of new systems on the market in the undert $20000 range too.
5. How hot is too hot? Great question!!! Despite the fact that many people say they can predict failure based on surface temperature, it is NOT easy.
If you'd like more information on temperature measurement, I have a short checklist on "Improving infrared temperature measurement" that I would be happy to send you (and other readers) at not cost. Our company is the leading training company for thermography; we do not sell equipment but have great contacts with all imaging and spot radiometer manufacturers.
I hope this response, though lenghtly, is of help.
Snell Infrared www.snellinfrared.com