I don't have any problems with responsiveness or battery life.
As for battery life, it depends entirely on where you live. I experimented on it for months before finally figuring out that well over 50% of the power draw on the system is the data network (mobile network option when you hold down power). If you have it on when you have really weak/no reception, the phone will burn through the full battery in about 4 hours and it's pretty simple to lose 20% battery in 15 minutes. If you always have a decent connection, your battery life will be fine, if you happen to live in a place where you have holes in your coverage (e.g. NYC urban canyons), battery life is terrible.
After realizing that, I set up a set of Locale rules to shut down the network when I'm on the wireless network at home/work and to shut it down when I lose signal. Combined with the undervolted kernel, I normally get 48 hours on a charge for my normal use (~350MB/mo).