Here's something I found that's kind of interesting. Granted it's based on a small sample size, (Drafts between 2000 and 2007) and it involves players making the Pro-Bowl which can be bullshit because of players being selected based on name or team recognition.

Average number of Pro Bowl selections per year by round drafted from 2000 - 2007 (8 yrs.)

1st Rd. - 12.5 per year
2nd Rd. - 5.5 per year
3rd Rd. - 2.0 per year
4th Rd. - 2.375 per year
5th Rd. - 1.625 per year
6th Rd. - 1.5 per year
7th Rd. - 0.75 per year

UDFA's - 4.125 per year