I definitely agree with Russ. Record EVERY little thing.

With my MZ-N707 from Sony and most newer MD recorders you have MDLP which can give you 74 minutesx4 = 296 minutes, or nearly 5 hours of recording time.

It uses AA batteries. I don't bother with the NiCd which came with it. I prefer to use Alkaline batteries. I KNOW I can get roughly 5 or 6 hours on one battery. Some of the newer ones use specially designed Li-Ion rechargables to keep the profile small. Personally I don't like the idea. I prefer to have a second battery handy to swap in when I need it. NOT a recharger which can take 4 to 10 hours to recharge.

You NEVER know

Anyway, it's a good deal. Personally, I don't speak much into microphone when doing field recording. It will give a much more natural feel to the informant's sound. If you keep starting and stopping, the informant will be made aware of the recorder. My recommendation is to explain to the person what you are doing, set things up, start the recorder, and as Gargoyle says, give the date, location and informant's name and what you're doing and then EVERYTHING else becomes a conversation. Try NOT to look at it again until you're finished. As your conversation becomes more relaxed, the informant will be more natural about things. Try to get a conversation going before the recording to relax the informant.