shot,
I regularly shoot High Master during qualifications with my dept. Scores are 492 or higher (out of 500) on a 50-rd. course with the IL. PTI target. (10-ring is a little smaller than a 3x5 index card.) Of the 50 shots 12 of them are fired from the 25 yard line. To be honest I miss as much at 15 as I do at 25. (Lack of focus on my part, I need to do better...)
Another anecdote - My best friend from High School and my shooting mentor's son who was into guns (imagine how we became friends?) was one of two people whom I respected as a shot good enough to regularly beat me. He has moved away, but came back a few years ago and we went to the range. He had just acquired a nice S&W 745 and I had my Glock 21. (Both 45ACPs.) We went to the back-yard range and started shooting, and it became apparent I was out-shooting him pretty regularly. (We were shooting the same ammo.) We traded guns, and both of us could shoot the Glock 21 better than the 745. I will admit that although all Glocks are pretty accurate, there is something about the 45s that they seem to naturally shoot more accurately. They are the only Glocks with OCTAGONAL rather than HEXAGONAL rifling, so it may be the form of the rifling...
All that said, I'll admit that I ALWAYS shoot revolvers better than autos. Regardless of brand or caliber. (My qualification scores when we carried revolvers was anywhere between 495 & 500 - on average 5-10 points higher than when I shoot any auto.)
Also, I do have some autos that will out-shoot my Glocks, but not by much. My most-accurate auto (and the only one that matches the accuracy of the revolvers) is my Walther P88C. It regularly chews a hole a little larger than a silver dollar at 25 yards with a couple mags of 9mm. My Glocks don't match that, but neither do any of the Kimbers or Colts or Sigs I've got or shot.
Before Glocks existed, I was a 1911 man. (Back then, there were no Kimbers -other than rifles- or any other custom-from-factory 1911s. You shot a Colt or Springfield Armory, and they were pretty much like the commercial or military models that had been made since the 1920s... To get anything like a Kimber you had to pay $2000 to a custom 'smith and turn over your Colt and wait 12 months. Therefore, all of my 1911s are and were military or commercial models without the bells and whistles.) When I started toying with the Glock (and other non-1911 autos) I couldn't shoot them anywhere near as well as a 1911. When I finally decided the Glock had some great qualities and would be what I would switch to when our department went to autos, I started shooting it as religiously as my 1911s and revolvers. It was only after near-daily shooting and dry-firing for 6 months that I adapted to the Glock's trigger pull and started shooting it well. One other thing I changed was the sights. Big, blocky, plastic sights do not work well for me. (They were designed to be quick-pick-up combat sights, but I prefer something with more precision.) I changed them out to a set of Novaks, and that picked up about 15 points on my qualification score.
Glocks are VERY inherently accurate, but they're trigger has a unique feel that DEMANDS getting used to and adapting to, or it's very difficult to shoot them well. But, given the commitment to time and practice, they can be shot as well as any other pistol out to 100-150 yards.