I am really, really slow.
Any necessary background: I am 23, female, 180 lbs (5'11"--so not seriously overweight, but a little). I have always been pretty terrible at all kinds of physical activity. I have a cheapish hybrid. I put about 250 miles on my bike in 2005, and I've done about 170 so far in 2006. And I am slooow. This morning I took 70 minutes to go 12 miles, over mild hills, and that's pretty typical for me.
I know I should have a better bike, which isn't really a financial possibility for me right now, and spandex (I had bike shorts under jeans this morning, because it was cooold). But I think mostly it's that I'm just not very good. On the flats I usually push a gear of 70", and can't go much higher while still keeping my cadence up, and even mild hills send me into my lowest gears.
I thought it might be just a matter of time, but I've been doing consistently about 10 miles every second day (my endurance is not so great either) since the beginning of the year with no improvement whatsoever, so I think I need whatever advice you might be able to provide.