Just a real real quickie related to WordPress here, not Magento. If you find adding comments in wordpress causes a blank page – try disabling akismet. If that fixes it, it probably means the domain you were using to test with in the comments field has been marked as spam by Akismet. WordPress serves up the blank page as a feature to prevent spam bots. No errors were logged though, so it made it a bit tricky to figure out what’s going on.
There are loads of other people with this problem, or variations of it online – googling around there semeed to be a lot of confusion – my sugegstion is to try disabling akismet first.
Other possible causes though I found and tried before getting to Akismet: Old theme with incorrect comment form on a newer version of wordpress – compare it to the default theme for your version of wordpress. Caching – try disabling your cache if you use one.
Hope that saves someone some time. Magento content coming soon, promise…