I'm currently freezing whenever I go into a town, there might be more adddons doing this, I'm currently checking mine for ones that do it.
Update: Well, it's not any of the big addons like fubar, pitbull, bartender, cartographer etc
Update2: I have it down to a very few addons now, will update again when I find out what one.
Update3: Looks like it was the addon Simpleminimap.
So deleting your wtf folder and your add-on folder will fix add-on issues. However it does so by completely removing all your add-ons. The WTF folder is your ui settings, chat windows, icons, add-on settings etc. You delete this and most if not all your add-ons will default to the original settings. This includes your graphics, ie resolution.
The add-on folder is all your add-ons. So deleting this will remove all your add-ons. If you delete this without deleting your wtf folder you'll keep the settings but any add-ons still won't show up.
The proper advice isn't to delete your wtf and add-on folder. What you really want to do is to copy it into a backup folder. I always recommend this before logging on after a patch. Copy both the wtf and add-on folder into a backup folder. I recommend something like 'c:\wowuibackup\080328\'. So you have a backup folder with a sub-folder with the day's date. That way you can remove the wtf and add-on folders from the wow directory. This will leave you a backup of all your settings in case you need it.
Another thing I recommend is to backup your wtf and add-on folder after you installed all your preferred add-ons and set them all up how you want them. That way if something goes wrong and you lose your settings you can always copy it back over.
The reason Blizzard gives this advice is because add-ons can cause errors, crashes and other issues, all of which are out of Blizzard's control. It's the equivalent of 'reformat your hard drive'. Yes, in some cases it might be the very best thing to do. In most cases it's not.