If I've done my math right based on Shog's answerShog's answer, no it hasn't made a difference.
60 days prior to registration:
Registered Users:
877 bad questions 948 good questions 1825 total questions 48.5% bad questions
Unregistered Users:
182 bad questions 57 good questions 239 total questions 76.15% bad questions
Total:
1059 bad questions 1005 good questions 2064 total questions 51.3% bad questions
60 days prior to now:
1314 bad questions 1104 good questions 2419 total questions 54.32% bad questions
If anything, it looks like our percentage of closed, deleted, or downvoted below 0 question rate has gone slightly up since we started requiring registration.
The reason for it going up may be unrelated to requiring registration though, as 2 sets of data isn't really enough to draw any solid conclusions.
