we seem to be in the same boat as you (doh! just looked at your signature - jaina's only 4 days older than nathan :wink: )
jaina's been going through a period - for a couple months - where she was an absolute bear without the nap, but kept trying to stay up anyhow. she got to the point where she would refuse to sleep at the sitters' on the days she was there all day, and i would pay for it that evening.
during this time, she'd still been sleeping for me, but the time has been getting shorter. instead of 2pm-5pm, she started going down later & later, until it was 3pm - 5pm. she'd always crash, and she was a bear when i woke her up.
then within the past couple of weeks, she started not even falling asleep until around 4pm, and was an absolute crazy person when i woke her at 5pm.
she's also started trying to stay up later than 8pm in the evenings, using all sorts of stalling tactics. when that doesn't work, i can hear her playing in her bed. some nights it's been after 9pm when she finally conks! :shock:
so (today!) i just didn't have the energy to try & wrangle her into bed. she's potty training now & getting her in a diaper for naptime has turned into a power struggle. she seems to be fine.
i'm sure there are days where she'll need a nap, but she seems to have slowly. i'm also hoping that with no nap she'll be more tired at bedtime.
hope something in this ramble helps.