Nowadays probably less than 1%.
Before Silk Road was closed down, and before there were that many BTC vendors, maybe over 50%.
Yeah, but really, do you think that just because one site was shut down that ALL of those rich-ass drug dealers, hitmen, and addicts all said in harmony "Aww, well, I guess I'll have to go back to my 9-5 job. It was fun while it lasted."?
Edit: @Prizz, I know!!! Everyone just thinks that Bitcoin, VPNs, and everything that is untraceable is just used by the common man. It's just not so.