Dear Mark. I have installed the mediawiki 1.21 and I am testing it.
More comments about installing:
1. Setting of default host is tricky: one needs to guess, that
for OS X, the correct value is 127.0.0.1. (as for Windows)
2. I think, the default setting should include the most popular
extensions. You may consider to include
Typing of formulas,
Use of images (including *.pdf), and
Citing of references
into the default installation.