Just finished Ultimate N00b Challenge, I did 10k on scout bots - got 24 BTCs in total, 2 just today. So they still drop - one every 400 kills from what I see. If you compare that with some historical posts it looks like drop rate is about the same. The problem is that drops are very irregular, today I got 2 from killing only 500 bots - but there were also times when I got none in 3k kills. I guess you need to kill a lot to converge to avg drop rate - 10k I killed is probably not enough too.