CoPs and Goals
Its hard these days to find anything new said on CoP's, but Madelyn Blair in an interview with KM Magazine made a great point about goals:

"If the CoP is over structured through specific goals that must be met, there will be no open space, and learning will be stifled. On the other hand, if the only goal is learning, the lessons gained may become so removed from the business goals that they can't even be communicated let alone acted upon. So, while it would be great to say that learning is the most important goal of a CoP, it must relate to the business goals sufficiently to allow for the lessons to be received and acted upon. "

This implies a timeliness to CoPs too - that even if what was learned was immesnely valuable in principle, its likely to be forgotten if it can't be applied soon after encountered. Just like all the training courses I've been on that faded before I ever got to apply the skills.

That said, a well-formed CoP would build up a degree of robustness that doesn't rely on shiftign around specific business goals: if its really based on practice then it's highly likely that its topic is relevant to the business because practice implies people are doing it routinely (unless that practice is Minesweeper). And if its a high-quality lesson, then it will be based on multiple cases that keep recurring, so the role of the CoP is to be custodian of that lesson until it becomes timely for a member to re-apply it.