I do just the opposite. I usually bottle my Belgian styles and keg everything else. I find it is easier to get the carbonation right in the bottle. The keg just foams at the higher carbonation level. Shelf life depends on sanitation, but there is also a point where the beer is in peak condition, and a point where it loses its zing. Sometimes it just dries out too much or loses its hop character. I think this depends on the gravity of the beer. I think a low gravity beer from 1.035-40 usually tastes best with 3 weeks of conditioning and then stays primo for a couple of weeks. After that is starts to go down hill. It is not infected, just past its prime. I usually make most of my beers in the 1.048 range, and they taste great for about 3-4 weeks after conditioning for 3 weeks. This gives me several weeks of good pale ale. The last gallon is usually not as good as the first 4, and I know it is time to make some fresh beer. Beers in the 1.055-70 range take a bit longer to condition to their prime point, but then they stay in condition for several months. Most of my saisons are in the 1.050-55 range, but ferment out to 1.002-6 so they have more alcohol and stay fresh longer. I usually brew 10 gallons a couple of times a year, and that is enough to keep me in Saison for the year. Keeping the beer cold also keeps the beer fresher longer. If it is sitting in a warm closet or garage, you had better drink it fairly quick or else it will oxidize or develop off flavors.