I have participated in NING and WebJunction for several years. WJ, I think, has been a great tool especially in the area of technology support, course, rural library sustainability, and for topical discussion. Mn-WJ is still developing, but perhaps it will come into its own in the next year or so.
I think these tools are a great way to connect with people of similar interests or concerns and for once, geography is not a dictator! I think WJ has been particularly useful in leveling the playing field and giving people every where the tools they need to do the jobs they do.