The only .NET wiki that looked interesting to me is FlexWiki. It is used by Channel9 and PInvoke.net. I had high expectations for it, but not all of them were met.

The project seems to be in heavy development and disorganized state. Its main web site runs on the wiki engine. All requests for help are done through the wiki by editing different pages and posting the questions on them.

The wiki supports both flat file data storage and MS SQL, but database support was introduced just recently. It seems to work, but I'm not sure how stable it is. The wiki doesn't support export (at least I found no easy way to do it).

FlexWiki does have support for dynamic topics, but it's limited. Only specific things are supported (generating a list of topics and sorting it). Additional extensions have to be written in .NET (a plus). There's only a handful of them at the moment, and that makes this wiki less attractive than other wikis (a minus).

FlexWiki authentication support is minimal. It's possible to configure it to use windows authentication, but that's mainly all or nothing. I would prefer to use database to store log-on information and to let people register. I also want to specify different access permissions to different pages.

The wiki seems to support skinning only through CSS. There's no support for templates or anything like that.

Conclusion

Originally I thought I would be using FlexWiki, but I changed my mind and decided not to. It's still too fresh and lacks a lot of features. It is developed in .NET and supports MS SQL, two big plusses, but that's about it really. Some of the dynamic topics support is interesting, but limited (compared to some other wikis).