Heat, heat is the enemy of all things electronic. As long as your PSU is kept cool it can last a very long time even when being run continually (I run all my PC's 24/7). As SteveSkills points out, even no name PSU's can last a very long time. Things that will help your PSU last longer; 1) clean the PSU out, when cleaning out the dust from your PC, give the PSU a little attention also, there are heatsinks and other areas to catch dust in there, keep those clean. When the PSU is unplugged from the wall it is safe (and I recommend this) to put the canned air's plastic wand down inside the PSU to work the dust out. 2) Keep load on PSU about 50% of it's rating. 50% is the magic number where almost all PSU's are at their most efficient, it is...