I would definitely say no to the compressed air canisters for cleaning components, because air contains moisture you're basically spraying tiny particles of water which can lead to shortcuts later, vacuum cleaners are also a big no due to static electricity. If you -really- want to clean it use alcohol with distilled water (50/50 mixture.) Using compressed air isn't really harmful unless you're really unlucky, but for durability I would be against it. You might have damaged the fan's bearings by blowing into it.
Remember that fans can slow down depending on CPU load, it's mostly a feature on newer motherboards (Intel EIST for example) but I'm just exploring every possibility.
As for a reasonably reliable temperature reader, have a go with Everest
There are a number of ways you can replace components, first check with your warranty if it's still valid. If not, just carry it with you to any random PC hardware store, I'm sure they'll be able to help you.
Edited by GotTeeth, 16 May 2008 - 12:11 AM.