The first thing you need to look for is rotten logs. Take a hammer and walk around the house taping on the logs. You will notice the difference in sound when you hit a rotten log. Corners and the bottom corners of windows are high suspect areas. Also, bottom logs on deck areas and logs that are close to the ground. If thereare rain gutters, you should pay special attention to the corners for rot. If the checks (cracks) in the logs are filled with caulk there is more than likely some sort of rot.
Plan on some sort of maintenance every year, Caulk/chink repair, stain touch up, and over all inspection for troubles. Most log home stains require a maintenance coat of clear or top coat every 3-5 years.