I'm doing hour long rows these days also...got so busy yesterday that I was doing it at 10pm, watching March of the Penguins...kept telling myself if those little dudes can stand all that then I can row with 'em...got 12k + so felt good for an hour's work at my age and condition. I would have never guessed I could row 10k+ on a daily basis but am thinking of keeping this up now even after the challenge. I am better than last year too. Like you say, some fast ones inbetween are fun too. I'm working on the 'fat burn' so the long and steady is my main focus.
GO DUCKS!!! Fend off all challengers!!! GIRLS RULE! QUACK!!

Best Wishes to all out there...
Birdi