The past 4-5 hours I have experienced odd problems with WordPress.
Basically, whenever an action is taken that writes to the database (such as a comment or a post), it prompts the user to download the called php file. Everything else works fine (and it does actually write to the database), but it doesn't return to the previous page where it should be.
It's only started doing it 4 or 5 hours ago. The last time I did uploaded a plugin or change the template was last Friday, and even after disabling the possibly offending plugin, the site still has that problem (I don't think it is that, because it was working fine this morning).
The installation is at http://www.gospelrhys.co.uk try leaving a comment to see what I mean.