i have 3 of the 450w ocuk psu's that i got when they were on special for £13 to see what they where like.
i used 1 in an i3 build i did for a friend, i3 530, onboard gfx, 1 hdd, 1 optical, 2 80mm case fans, just really a surfing and pottering about machine and the psu is fine for that kind of thing.
i was building a spare machine for myself and put one in that to see how it would cope and it was fine with the original components, x2 6000+, 1hdd, 1 optical, 2 90mm case fans and a radeon hd3450 and the psu was fine for that also but then i put a 9800gt in instead of the 3450 and the psu fan ramped up and a noticeable humming sound started becoming more audible at which point a put in a corsair cx 400w which coped without a problem.
so from my experience i would say these psu's are fine for general machines with mid range cpu's and onboard or low powered gfx cards, as soon as you put in any higher power drawing components i would recommend getting something of a better quality and i would not myself use these in a machine that draws more than half of their listed rating.
i hope this helps.