Participating in any sort of forums or outside communication via company equipment during work is completely off-limits (often for regulatory reasons rather than draconian. For example, Hulu and Youtube aren't blocked because, while they're time-wasters, they aren't really venues for communication which has to be logged.)
I wonder how many people would be grouped in the "lurker" bucket not because they don't have an interest in this sort of thing, but because restrictions at work make participation require too much activation energy.