Slightly off topic this one. I have been a member of WPMU DEV for about 9 months now. Its a premium WordPress Theme and Plugin Membership Site. Initially I did feel the price being on the higher side. But as I started using the plugins I really felt the price is well worth it. There are lots of commercial plugin sites out there. But not all of them are good. Also not all these sites have the variety of plugins that WPMU DEV offers.
There are few plugins which are their flagship plugins. These include Membership Plugin. Frankly for an enterprising blog network, this single plugin is worth the entire membership amount. It has very strong functionalities and my online friends who are using them swear by it. Since I do not run a blogging network per se, I have still not used it. Another of their innovative plugin is Marketpress. This is their own shopping cart plugin and which is easily extendible for any payment gateway and has a host of features. Again I do not use it much since I love another shopping cart plugin and also because Marketpress is still adding more features and I honestly want to wait for it.
So what are the plugins I use most frequently. There are quite a few really. I love their Domain Mapping Plugin, Multi-Domains Plugin and WordPress Directory. Domain Mapping lets me map any domain to an existing blog in a multisite environment. I can also make multiple domains point to the same blog. Multi-Domains Plugin lets me use multiple domains for creating blogs on a single WordPress Multisite install. The best thing about these 2 plugins is that both of them have been enabled to work with each other. How cool is that 
I have used WordPress Directory for my friend’s intranet site. Since their network contains multiple blogs, the plugin helps in creating a directory structure for the entire network. Its simple and easy. I have also been excited by their Ultimate Translate Plugin. I discovered it last week and it is so simple to provide translations of your blog and also redirect users based on language. I am trying to implement it for 2 of my blogs.
They also provide themes but honestly I have not used them. For me I always have a mental block with using any theme. It takes me ages to figure out how to change the designs and I am still not comfortable with the child themes concept in WordPress. But I am sure you all will surely find a theme to your liking there.
The best part of the membership is their Upgrade and Support Guarantee. I joined them in pre-WP 3.0 era. After that WordPress had 2 major upgrades in 3.0 and 3.1 version. The guys at WPMU Dev have been very prompt and upgraded all their plugins and themes to support the newer versions. And not only this they informed us way in advance about the upcoming changes. What more can you ask? All in all, it has been a pleasant experience for me. If you are serious to start your own blog network or even a single blog, WPMU Dev Plugins are the way to go.
