Sorry for resurrecting this old thread. Just stumbled across it and figured I'd add my details:
4-4.5 miles or so each way (about half of it is streets and the other have is a nice off-street trail that was newly opened). Takes anywhere from 20-30mins to get into work depending on cross-walks/lights/traffic. In my area, sidewalk riding is permitted unless noted on signs, so I take advantage of that around the business park area as riding in the street feels super-sketchy. I got showed up bad by a dude on what appeared to be a mtn bike (at least, the tires were mtn bike tires from what I could tell). He got ahead of my be several hundred yards in a matter of seconds on a downhill... although he was riding the street and I was cautiously taking the sidewalk haha. And this is on a Trek 7700fx! When I was a lot more in shape way back when, I was *almost* able to keep up with a guy going pretty fast on a road bike.
Then for whatever reason, today I decided to try the "back way" into work which involves a rocky dirt road that cuts behind some business parks and parallels train tracks and gets to the barren end of the business park where there's a cul-de-sac and usually trampled fence or open/unlocked gates. As it would have, all gates were fixed AND locked, so I ended up lifting the bike over, tossing my bag over, and hopping the fence.... then realizing I dropped my sunglasses on the other side before all this. So one more hop of the fence. And I got a couple nasty scratches/cuts on my forearms from the barbs at the top too. Needless to say, it wasn't a very good "shortcut" so I'll never be doing that again (at least, until they actually open it up haha).