For what it is worth, there has been some quiet threads plugging away this week discussing a possible Google update that is going on. Many are watching some of the datacenters closely. SEOchat has the biggest thread and people are analyzing what is happening during this particular update. Many are either seeing their rankings drop or no change whatsoever. Some members are thinking it has something to do with devaluing reciprocal linking and others think its another reason to believe PageRank is dead.
An interesting concept that is arising from some of this is the possibility that many of the members of a single forum often trade links with each other and because of this reporting on Google updates is really not very reliable. Its a tad unbiased don't you think. Naturally forum members who all trade links with each other may be more receptive to possible negative consequences a Google update have or maybe they don't. Members exchanging links on forums is common practice, but I dont' think anyone has asked what the critical mass would be for such thing. Can you imagine all the members participating in link programs such as Link Vault and Digitalpoint Co-op? Reciprical linking? Good number of people I imagine. What happened if they all disappeared overnight? We know Google knows about these programs, and people have gotten penalized for use of such programs in the past. My point is while you can use these programs successfully, tread carefully and "diversify" you link building activity.