he fact is that they make software feel unprofessional
personal preference i guess, but i think it shows that it was programmed by people that were enjoying themselves.
First time somebody i installed linux for saw some similar requester he said: well at least they were having fun making this.
Maybe it even makes people actually read the requester instead of clicking 'ok' as fast as possible to get rid of it.(as i usually do on windows). But it shouldn't be overdone, just some of the requesters that pop up very rarely like; fatal error, syntax error, reboot now,software failure, etc..