Tonight I washed out a plastic peanut butter jar so it could be recycled. I had to use a LOT of hot water to get off the old peanut butter. Was this really good for the environment?

Using a lot of hot water by letting the tap run until the peanut butter is dissolved away is probably not too conservative a use of energy. What I suggest is you just half-fill the jar, add a few drops of detergent, replace the lid, and shake vigorously.

What's the matter with you guys? When we finish the dishes, we wash the recycle stuff - cans, glass, plastic in the previously used dishwater. We do not rinse them as we do our dishes. This involves ZERO energy cost or environmental damage. Just a little elbow grease, and we need the exercise.
We don't use a dishwasher. For people who do, there always seem to be a few things that need hand washing, such as glassware. Do your recyclables then, and in the same way: do proper dishes first, then recyclables.