if you want to run Windows Vista.
Another reason not to run Vista. To add to the already long list :Þ
Why? Well, I always check updates manually. In installed a recent version of Vista in a VM to keep my knowledge up-to-date a bit better on what they renamed everything to in this piece of junk so I can at least help people if they have questions (although my advice remains: run windows XP Pro, and do not install MSIE7 (or uninstall it if they force-fed it to you through windows update)).
When selecting a bunch of updates needed, and leaving stuff not needed unselected, I was presented with the following screen (click thumbnail to enlarge) and, no kidding, as you can see, a download size of more than 2.5 GB! ... WTF are they thinking?
Now imagine having one of the many Internet subscriptions that have a monthly download limit. 1GB is rather common for those. Pay-per-MB for anything over it... and having Vista installed "default" meaning all this kind of stuff happens in the background without you even knowing it. Just the windows updates alone (not counting any driver updates or "recommended" updates that I didn't download but is checked by default as well) would put you 1500 ticks over your limit, imagine the bill for that :P