First let me say, I started off with the Moultrie D40 and well to put things litely, it was junk. I couldn't get it to take pictures, keep the date, etc. so I called Moultrie support and the woman was very understanding. She said for $50, I could upgrade to the M40 and I wouldn't be sorry.
Man they were not kidding. Much better camera. Battery life is great. Out for 3 days and it's still at 99% (the d40 would be have been below 50%) the date/time, temp, moon phase are all great. I also liked the fact it has software upgrades available which can be downloaded from their site.
Here are my first pictures of deer. Should be nice in a few years.