[quote name='.Wolfie' date='18 February 2010 - 11:42 PM']
...Next, having it per group could be very beneficial. Enable it for admins and mods, but disable it for everyone else (for example). On an extremely busy board, this might cut down on resource usage. After all, having 1000 people online at once (which some boards have), if a lot of them are doing previews, then that's a major resource hog.
That's exactly what I would suggest, if this option will consume many resources I would rather not have it, in my case i have a large site and most part of the day i have 1500k + users online, please think about the people who have very busy sites.
Do not misunderstand me is a very good feature, but should have the option to turn on or off.