There's a thread in the tutorial section about this- I think the title is something to the effect of 'Don't sweat the small stuff.'
The other night during the Detail 202 session, we hit Sawmill to look at examples. There's a decal of tire tracks that gets clipped oddly because it hits the edge of a brush. There's a building that has no door anywhere on it. There's nodraw edges, walls that stick out of roofs, and badly aligned textures. Similarly you can hit 2Fort, or Goldrush and find areas that aren't right.
But how many of these get noticed in actual play?
When KotH first hit, the servers I'm regularly on ran Sawmill KoTH regularly. There'd be a good dozen rounds of play there every day for me. I ran past that building that has no doors over and over and over again- I never noticed. Why? I wasn't really worried about it. I was more concerned with the other team. Similarly I never heard anything about it on chat- and the comments in the mapping class suggested this wasn't isolated to the servers I play on.
Little imperfections, and even larger ones, aren't that big of a deal. You're likely to notice them when you're staring at them with nobody shooting at you, but in actual play, a lot of people are going to skip the little things. They'll probably notice the big ones, and depending on how you lay out your map they may run into an area and suddenly have dozens of details to take in at once, where they'll stop and appreciate the work you've done- but most of the time, the issues they're going to care about are the ones that would come up if everything was rendered in dev textures:
- Are there enough ammo boxes and health kits?
- Do I know where I'm supposed to go?
- Can I get there (wherever there is) quickly?
- Can I defend/assault that objective effectively?
Past that, I'd guess that 90% of the people who'd notice the details are your fellow mappers.