How much of a difference in workout intensity does riding a pedal-forward bike make? My wife has a pedal-forward frame that looks really comfortable to ride.  I have a older road/mountain hybrid that's a little hard on me and would like to start riding again to get a little exercise (and hopefully lose some weight).

How much less intense a workout can I expect if I move to a pedal-froward frame?
I take it your wife has an Electra 'Townie' style bike with the easy reach to the ground, the high bars and the pedals a little further forward than normal.

Sat down, in the saddle, these bikes do present you with a mechanical disadvantage going up hill as you have not got all of your weight over the pedals. Hence, when going up hill you need to be aware of that, to take a lower gear and inch your way up the hill much like how a recumbent cyclist has to...

...or get out the saddle and pedal with your weight on the pedals as if you were sprinting. Works the same as on a normal bike.

There is also 'easier' handling that is less twitchy but with a bigger turning circle with pedal forward design. So I don't think it is simply a question of workout intensity that you are looking at - ultimately you can put in as much or as little as you wants to...

Many of the 1950's design commuter bikes are effectively 'pedal forward', only when the drop-bar racing bikes with ten speed did the relaxed geometry of a classic 3 speed go out of fashion. You can refurbish an old 3-speed with some modern tyres to get the comfy riding style that the likes of 'Electra' offer.