I tend to really push it if a lot of people are on the course and I need to get by. It is impossible to follow the intervals to a T in that scenario, so that helps improve my time too. I got sore and a bit more tired doing the longer intervals and at DL in 2010 heard Jeff talk about the 30 second intervals and how great they were so I thought why not try it? (Granted you aren't supposed to do anything new come race day, but I guess it sounded so good, I couldn't resist) It is so much easier to gun it for 30 seconds than for one minute or two minutes!

I am faster during the races than with my training too. But, I train entirely on the treadmill which keeps me at an even pace. Plus, it can be pretty boring.
If you haven't tried 30 second intervals, I would recommend just seeing how it works for you. It may end up working out a lot better than you thought it would!