going to Ebay and looking at their US coin market (anyone can duplicate this, btw, but the numbers are constantly changing and are a snapshot in time) and looking at stats, I got the following
total coins for sale: 562,816 23.71 % graded, the rest were raw
PCGS 62,789 11.15% of total, 47% of graded coins
NGC 57,734 10.25% and 43%
ANACS 9,149 1.62% and 7%
ICG 3,801 0.67% and 3%
There are a few other grading companies like SEGS and PCI but their combined total were less than 1K coins so I didn't bother including them
There clearly is room to grow as less than 1/4 of all coins for sale are graded. Some consider any coins other than PCGS and NGC to be raw.