Finally back on CBid after being offline for a few days, and I see this thread. Just started rowing on a Concept 2 again after listening to "Boys on the Boat" on CD.
Pro: great work out, balances whole body. Especially when you are super one-handed like I am-use my left hand for almost nothing.
Con: pretty expensive ($900) unless a convenient gym has one. Potential to f'up back if you don't learn and use good technique.
Fortunately the base gym .3 miles from my desk has two, and base near the house also has multiple gyms with rowers.