My experience has been good. I don't have much programming talent, actually none at all, and the fact that we can build a robust community that allows me to communicate easily with all members is very helpful.
I have added a couple features to our Ning site to enhance functionality and keep our dedicated members in the know. We gave an incentive for our community to sign up for email subscriptions through Feedburner. It sends an automated email (in HTML) with the latest site updates on our blog. Now I just update our blog and over 1,000 people are updated automatically. It helped build retention and keeps people coming back often. Plus the emails get into their inbox and not spam.
have heard good stuff about wildapricot - there is also buddypress - a series of social media plugins for wordpress mu - still in development beta, but its the only one I have seen that is free, completely open sourced, and backed by a huge developer community