I'm thinking of starting a wiki, probably on a low cost LAMP hosting account. I'd like the option of exporting my content later in case I want to run it on IIS/ASP.NET down the line. I know in the weblog world, there's an open standard called BlogML which will let you export your blog content to an XML based format on one site and import it into another. Is there something similar with wikis?
The correct answer is ... "it depends".
It depends on which wiki you're using or planning to use. I've used various over the years MoinMoin was ok, used files rather than database, Ubuntu seem to like it. MediaWiki, everyone knows about and JAMWiki is a java clone(ish) of MediaWiki with the aim to be markup compatible with MediaWiki, both use databases and you can generally connect whichever database you want, JAMWiki is pre-configured to use an internal HSQLDB instance.
I recently converted about 80 pages from a MoinMoin wiki into JAMWiki pages and this was probably 90% handled by a tiny perl script I found somewhere (I'll provide a link if I can find it again). The other 10% was unfortunately a by-hand experience (they were of the utmost importance with them being recipies for the missus) ;-)
I also recently setup a Mediawiki instance for work and that took all of about 8 minutes to do. So that'd be my choice.