  We present a simple spin evolution model that predicts that rapidly rotating
accreting neutron stars will mainly be confined to a narrow range of
spin-frequencies; P= 1.5-5 ms. This is in agreement with current observations
of both neutron stars in the Low-Mass X-ray Binaries and millisecond
radiopulsars. The main ingredients in the model are; i) the instability of
r-modes above a critical spin rate, ii) thermal runaway due to heat released as
viscous damping mechanisms counteract the r-mode growth, and iii) a revised
estimate of the strength of dissipation due to the presence of a viscous
boundary layer at the base of the crust in an old and relatively cold neutron
star. We discuss the gravitational waves that are radiated during the brief
r-mode driven spin-down phase. We also briefly touch on how the new estimates
affects the predicted initial spin periods of hot young neutron stars.
