I pulled the trigger on the Service Pack preview a couple of days ago & I can tell you sincerely: so far the system does seem to respond somewhat quicker & the overall performance seem smoother .... while it is easy to attribute this observation to some computer placebo -- one thing I can say is, there doesn't seem to be any deleterious effect from the update deployment & yes this is my Vista production machine, but this is not an endorsement for anyone to blindly install the update on their main machine -- heck, there are still folks out there that won't dare install the actual OS on their production machine & still rate XP as more reliable & better suited to their daily computing needs ;-)
As far as the banner is concerned: there actually IS a way to get rid of the desktop "Evaluation Copy" stamp. Although the procedure seem innocuous, I am not going make the assumption that it is ok to post it here. But let's just say it involves overwriting a file in the applicable system's X:\Windows\System32\en-US folder.
Now time-limit or feature crippling attributes are not really uncommon with computing software. Moreover, it is not the first time M$ had implemented such protocol nor will this be the last time. I also didn't think -- for a second -- that the move would deter the type of folks that typically adopt & install updates as such.
Odds are: many of them have been waiting for the "official" preview for some time & some may even have sampled the various non-validated leaks out there prior to now. So I really don't see the not uncommon move as a problem at all.
Finally the update does not strictly require any of the prerequisite updates mentioned above, although XpUser .... cough .... cough .... VistaUser is not flat-out incorrect.
I for one did not have to install any prerequisite update to get SP1, this is because I downloaded the Standalone Package & executed the installation that way & couldn't be bothered with the couple of additional reboots if I had pursued the Windows Update route for the Service Pack deployment. Now even if I had to .... it wouldn't have been an inconvenience of a substantial magnitude anyhow, since rebooting is often an integral part of many software installation.
If anyone's interested: the direct Standalone Package links for the x86 & x64 Service Pack preview are below.
Vista Service Pack 1 RC - 5 Language Standalone Package
Vista Service Pack 1 RC for x64 Based Editions - 5 Language Standalone Package
Vista Service Pack 1 RC - All Language Standalone Package
Vista Service Pack 1 RC1 for x64 Based Editions - All Language Standalone Package
Good luck guys!