I've done 3 computers, the first, a Sony Vaio, had windows update stop working. I found 3 fixes online, the first 2 I tried didn't work but the third from a MS sight did.
The other 2 computers seemed fine though.

this is the one that worked " regsvr32 %windir%\system32\wups2.dll "
Just copy to note pad and run it.

I have installed SP3 on 2 of my computers and haven't noticed a difference.

I ran SP3 on an old computer,and a new one.I haven't noticed any differences in performance!

There shouldn't be any performance difference actually. iirc sp3 is only a set of hotfixes and security patches with a few extra Vista feature add-ons

anyone with a bad experience doing update?

I just heard that it is same but it little bit faster then the SP2