I have no idea why different people would ostensibly and variably beseeing GMT-1, GMT and GMT+1. vBulletin is definitely configured for GMT with daylight saving enabled (i.e. +1 at the moment) right now and the time stated on the page is completely generated on the server side and self contained in the page HTML and not at all dependent on local configuration settings on the users's PC. All I can suggest is clearing your cache and/or pressing Ctrl-F5 to force a refresh and see if that makes any difference.