I'm probably in nearly the best shape I've ever been in. Weight training two days a week can take as little as 10 minutes to do can be really effective. I've basically doubled my bench press since the fall. Cardiovascular improvement seems to take place more slowly; my pulse when running 3 miles in 30 minutes has only dropped a couple beats per minute (I use a heartrate monitor).
I've read that it's a good idea to mix leg exercises when preparing for a long hike. I do a good mixture of cycling and jogging to work both the fronts and backs of my legs.
Yesterday I went out for a run outside instead of using the smooth track at the gym. I decided spontaneously to try running on the rocky bed of the railroad track. I figured that was about the closest I could get to hills here in central Michigan. The next day, my calves and ankles can testify to the effectiveness. It seems to be a great exercise for building foot and ankle strength. So, maybe the best place to train is to find the worst possible place and try jogging there?:) Like a furrowed and lumpy field or a railroad track (be sure to take off the MP3 player, though).
To be honest, I don't harbor any illusions about the effectiveness of my training. It's good for comfort value and to feel good about myself. But ultimately, after a couple weeks into the hike, we'll all pretty much be in our optimal cardiovascular shape, and my upper body muscle mass will have begun its inexorable decline. Woohoo!