I would be interested to see a follow up post after the honeymoon phase ends. I switched from WP to webby, loved it at first, but will be reverting soon. Static is faster, but php is fast enough for most blogs, and WP is full featured.
We have been using it for about 3ish months now and have not run into any issues. It is conceivable that the blog would eventually move over to a real CMS (not wordpress) once we have a need for dynamic content, but the website will stay static for the foreseeable future.
Same thing, but I switched from WordPress to webby to Movable Type. It's somehow easier for me to make posts in MarsEdit and publish them immediately rather than creating a new text file in TextMate, writing, then going to terminal to type "webby deploy".