I usually don't get distracted mid-set, but have (literally) walked into posts or tripped over benches when using the patented "check them out indirectly in the mirror so you don't get busted" move. And yes, it's "posts" and "benches" - plural. My personal best (worst?) was a hat trick - tripped over a bench, clipped a post with my shoulder, and walked into the front door of the gym while leaving in the same workout scoping the same babe. I got busted on the door...she heard the impact and subsequent shout of "fucking dammit!" from halfway across the parking lot. All I can say in my defence is that she was REALLY hot, wearing a bikini top (doing flyes) and spandex shorts (that didn't quite cover her J.Lo-esque glutes), blonde (I have a weakness for blondes) with a perfect tan.
My current gym - a/k/a "the dump" - has few women, and not much quality in the group, either. Helps my workouts, I guess, and I get fewer bruises too.