My gym routine is always kindof the same: go to gym, hop on treadmill, insert headphones, run at set pace for 5 miles, watch TV, try not to look at how much time I have left, finish, stretch, shower. It allows me to zone out, decompress, get a good run in and notch another work out. I have always read articles "Ways to make your treadmill workout exciting!" and things like that and they all universally recommend interval training. I have some experience with intervals on a treadmill when I was following the FIRST program for last marathon. FIRST is the "Run Less, Run Faster" philosophy, but the runs are really, really hard.
Last night I thought, eh,what the heck I will run some intervals. My plan: 1 mile warmup, then half a mile fast, half slow. In other words a 4x800. I tried to program the workout into the treadmill, and gave up after 3 minutes of fiddling. I would just do it manually.
Wow, it was a real kick in the pants. Overall, I went the same distance in a pace about twenty seconds per mile faster (so really not that much difference; for treadmillites, that is a 0.3 mph difference, or the difference between running at 6.7 and 7.0). I was completely spent, and even exhausted. Went home and just about collapsed. It also reminded me how hard the FIRST workouts really were.
Just goes to prove the old saying: don't just workout, train for something.