I have an older bowflex (PowerPro, before Nautilus bought them out) and love it. Lost 40 - 45 pounds in 3 months (each day alternating between the bowflex and inline skating). Put about 25 of it back on after getting married (I can't use it regularly anymore, and my screwy metabolism (thyroid?) won't let me cut back much on food intake).
I like it better than free weights because I can push harder without worrying about having a spotter - completely safe workout when alone. I absolutely hate gym equipment - the exercise machines never have the right geometry for my body (long waisted, broad shouldered, so I have short arms and legs for my height). The Bowflex never has that problem.
40 minutes for a good workout is about right for me. The trick (as with any home exercise equipment) is that you have to actually be committed to using it.
I'm more leary of them now that Nautilus has bought them out; if they have turned it into a "power rod" resistance Nautilus home gym, I would pass. If it still has the free-form cable/pulley system, it would probably work great.
edit: I forgot to mention that the "rowing" ability is completely worthless. The seat is not rigid enough to stay off the rail. The center of the seats drags along the rail and the resulting squeal is loud enough to hear outside the house.