Jan is making great extensions (look up everything named "Phoca"). It seems that his programming always is clean and simple.
My wish for this component is that there should be more different ways to show the galleries. There a few, but most of them are only slight variations.
After testing several guestbooks, I decided to use Phoca Guestbook because it works without any fuzz.
You can edit the captcha tables to remove letters and numbers that are easily confused like 1/l, O/0
Sent an email to the developer and got an answer in about three hours - great support!
There is one field for allowed file types and another one for prohibited file types - but they are not connected. So you may actually end up both allowing and denying the same file type if you are not careful.