On the baby trailer issue: my kid does not weigh that much and the trailer is pretty smooth to pull. But yeah, it cuts a full 2 mph out of my average speed. Oddly I don't find it to be too bad on hills (not that I ride many hills) -- I usually go about 2-3 gears lower than I would without the trailer, which is not as much as I'd expected.

It's wind that kills you with the trailer. You really feel the headwinds and the tailwinds aren't as nice as they are without a trailer.