In a perfect world, it would be 6 times a week. However, whenever I get up to that level, I tend to get ill, so it never works out. Now I can only do a couple times a week if I don't want my immune system to crash.
4-5 times a week. One day of strength training. The rest is either running, swimming, cycling or some machine or other at the gym (elliptical, etc). I love this time of year, when there's enough sunlight to go for a (fairly) long bike ride after work. Did that today and it was AWESOME.