In my sterstest I found ou that it did not heat up much don´t remember exact readings but it was below 50 celsius. The PSU it self is quite efficient so most of the heat comes from the power brick attached to it.
im talking under **extreme** loads.
here is my deaktop config:
PICO 120W
A1200 desktop PPC 268Mhz with Bvision,128Mb ram,
indivision ( runs on seperate 3.3v from PSU )
elbox eide mkIII.
this is my cofig at the moment and the PICO 120W PSU is very hot on one side,i cant keep my finger there,so it must be around 50 to 60c.
this is with floppy drive,sound card and extra 128Mb of ram not attached.
all im saying is as you put more and more load on the PSU watch the temperture because it mounted under the floppy drive... in other words you don't want to be heating up the floppy disc if one is inserted.