Foggyballa gave a good answer about the concept2 site. Rowers are also very good for tabata/intervals as there's an immeidate turn of pace, not like treamills that take a while to get there.Do you have specific workouts you all do on them? I often fancy using them at the gym but get bored after 5 minutes.
I used a rower to go from 21 stone down to 14.5 in about 9 months IIRC. Everyday I did the same interval routine:
3 minutes steady warm up
1 minute flat out
2 minute recovery
1 minute flat out
2 recovery
.......for 20 minutes.
I got to a half decent standard, my 500m PB was 1.24 or 1.26, I forget.