Commuted fixed today, 1st time. Great fun, same time as geared (door-to-door). I had been shaking it down w/in a few miles of home since the weekend, had time to settle the following concerns:

1-could I go as slow as my son - yes, more easily than freewheeling it turns out
2-maybe I need a bigger gear for the hills I have? - nah, except for the 2 downhills that end in red lights most of them I can push as hard as I care to just to build up some momentum for the coming ascent, which I wouldn't really want to tackle w/ any bigger gear than the 42/17 I chose.
3-will this tight turn offroad thgrough a mudtrap at the peak of a hill circumventing a gate prove a problem? - no, basically for the reasons outlined in 1&2, going uphill will scrub enough speed to take any tight turn and in fact it's easier maintaining s-l-o-w speed anyway.

Three other things: I really dig a rear brake so my legs don't have to do all the work of slowing the rear wheel, I love these tektro dropbar v-brake levers, and I can't believe I went for 32mm tires I need to shop for some 40+ ones.

Finally, I managed to jam a days' worth of crap (food, clothes) into a bookbag/satchel thingy w/ a shoulder strap that is a bit too long, so I think I will continue to resist a rack, but I need a bottle cage to carry that coffee cup.

edit: my soon-to-be 8 yr old is extremly conservative, doesn't like change, still loves the 16" bike he outgrew last year and regrets giving it to a 4 yr old friend, but this morning he yelled out 'I love this bike' about the 20"er he's had since last summer, he was surfing root heaves in the pavement and trying to catch air, he was definitely thrilled.