This may or may not come as a surprise to some of you, but the scale in Paintball2 is off. By a lot. According to id, 1 foot is 8 units. This is a bit short and would make the players 7 feet tall. It works OK for quick approximations, though, since there is a grid size of 8. In reality, a player would be closer to 6 feet tall. That makes 1 foot about 9.33 units, since the player bounding box is 56 units tall. According to my quick google search, the average male American height is more like 5.8 feet tall, making 1 foot about 9.66 units. This works OK. We can just round that off to 9.6 and have 1 inch be 0.8 units.
Now, think about the size of things used in maps. Barrels (oil drums), for example, are typically 64 units tall and 48 units in diameter. That would make them over 6 1/2 feet tall and 5 feet wide. That's bigger than some of those inflatable cylinders that can cover standing players. In reality, you can crouch and shoot over a barrel. They're only about 32 inches high. That's about 26 units tall.
Here's a shot for better reference:

You could fit a pile of real barrels inside of one Paintball2 barrel. 26 units is kind of hard to work with, though, and real barrels do vary in size. I think 32 units is probably a good height. Then you can just scale the texture to 0.5, align the brush on a 32 unit grid, and be done with it.
Next up is ladders. I'm just reusing a reference shot from SkateR's in-progress map:

Believe it or not, that 16 unit thick metal part of the ladder is realistically about the width the whole ladder should be. That's about 1.67 feet wide. SkateR's current ladder (along with ladders in many other maps) looks to be 96 units wide. That's easy math. If 1 foot is 9.6 units, the ladder is 10 feet wide. The thing that keeps it from looking too crazy is the fact that the rungs are about 10 inches thick.
These are just a couple examples of disproportionate things in maps, and any mappers out there might want to take them into consideration when developing future maps. It would be cool to work on making things a little more believable.