The communication, representation, synthesis, and reconciliation of experience and recommendations is in some ways an entirely orthogonal problem to that of group formation. They are both something that might be called "applied psychology/sociology", insofar as we are trying to construct, formalize, and implement practical theories using agents as assistants. However, while having some kind of information about potential group members is useful, reputation is useful in other venues as well, and need not have anything to do with group formation.
That said, it strikes me that the problems of group formation may well be more of a can of worms than I really want to address here.
For what venues is information about reputation useful, and how will it be used?
How much do reputation agents help under adverse conditions:
One thing that people are going to need to do--and should be able to do-- is to create their own domains and criteria for evaluation (and perhaps specify their relevance to other domains, i.e., if someone is a good recommender for car repair, this may mean that they're a good recommender for tractor repair). The problem is, of course, that unless people use the same terms (and in the same ways), that their agents won't be able to meaningfully communicate about them. (If I talk about "car repair", does it mean the same as your "automobile repair"? How about her "motor vehicle repair?") This could be viewed as a more profound (and perhaps subtle) form of the problem of reconciling recommendations from people that don't have the same prioritization. How can, or should, this be resolved?
Related question: should there be prefabricated sets of criteria/prioritizations for domains as they are created?
We need some way of merging evaluations and recommendations into a single opinion in order for recommendations to be meaningful at all. Perhaps this means that we can use a similar process to combine evaluations from several people into a single 'consensual [in the sense of 'consensus'] opinion'. This may inform our consideration of reputation agents as facilitators of group formation. See also the concept of the "distributed resume", mentioned above.
If reputation agents are informing the decisions of people engaging in club formation, what protocol is to be used to determine how the groups actually form? (It appears that no matter what mechanism one uses for determining group preferences for inclusion/exclusion--unless perhaps every time someone shows up, all current group members vote on the membership of all current group members (an n^3 algorithm!), group members are not created equal, since the later you show up, (a) the more people must pass on your inclusion, and (b) the fewer members in whose membership you will have a say.)
Since reputation is not necessarily the same thing as a list of characteristics (but rather a subjective perception of certain of those characteristics) this may be irrelevant...but it's worth considering: the best trading partner is not necessarily someone whose characteristics and preferences mirror your own. In particular, trading works best when the two people trading each have different things to offer (generally speaking, although there are exceptions, such as "I'll scratch your back if you'll scratch mine"). On a related note, it may be that the best groups for some kinds of tasks are those that have a certain amount of heterogeneity in skills, attitudes, and so on.