JesterMagic - 9:41 pm on Apr 23, 2013 (gmt 0)
Thanks for the replies.
@TheOptimizationIdiot - For the forum posts at least Google always changes the meta description as far as I can tell. But ... to be on the safe side I have just turned off using the primary meta description if none is given for the page. My rankings have been hurting so I might as well give this a go to see if it improves rankings, even though I expect lucy24 is right and it will probably not really make much of a difference.