I agree that it depends on the person. However, there is nothing wrong w/ goint 7 days a week. The human body adapts well. One thing you SHOULD do is always mix up your workouts. For example: do not always do flat bench bench presses when working out your chest. Change it up. On Monday do flat bench & flat dumbells...on Thursday do incline bench & peck deck machine. Same w/ all muscle groups: bi's do preacher bench & standing dumbell one day, then do standing straight bar & standing e-z curlbar. Same w/ cardio: I like to run but I never do the same distance or intensity each time. Some days I'll sprint 3 miles as fast as I can go. The next day I'll run a slow 8 miles. The next day I'll do a mid-speed 4 or 5. The next day I'll do a full sprint 1.5 miler. Some days I'll sprint one mile, walk a half mile, sprint a mile, walk half, sprint one and walk half.
Basically, you can "workout" everyday if you want. Just change it up. If you do a heavy, heavy chest workout on Monday lay off chest until next Monday. Or if you do heavy legs, do light legs 4 or so days later.