I got the Strava cycling app for my phone recently and started using it on my commute, and found out that my daily route has several popular 'segments' that have been recorded and ridden by many cyclists in my city. They are pretty much the most challenging parts of my route - major hills, and pieces including smaller hills, stuff like that. The app automatically added me to the 'leaderboard' for these segments - of course, since I didn't know they were segments and I was riding with full panniers, I started out pretty close to the bottom of each leaderboard. But once I realized where they were, I started trying to improve my time. They are short - a mile or less - so I can put some effort into them without killing myself for the rest of the ride, and I started setting PRs pretty much every commute, and moving up the boards pretty quickly. It's changed my attitude toward the 'hardest' parts of the commute - where I used to just trudge up the hill in a low gear, now I attack them in as high a gear as I can manage, sometimes standing up to add speed. Made them a lot more fun, it's increased my speed overall and shortened my commute time, and I'm already feeling a difference in my fitness level, even though it's only been a couple of weeks. I don't know if anyone else has tried this, but it's really freshened up my commute, which frankly was getting a bit stale. I recommend it.