Personally if I wanted 24/7/365 service from a drive I'd get one of the WD "AV" series drives.
as they are intended for constant run/constant write for surveilance video.
and some of the places those drives get installed can get pretty warm...
because they want secure and "cool" gets forgotten
I don't know what market the VelociRaptor drives really fill, technically, but I know the "appeal" to have somethoing fast is mostly emotional because for the vast majority of people the difference in speed is undetectable.
And I just ordered a drive a few minutes ago... a WD Scorpio Black 750Gb 32mb Cache drive... NewEgg had them on free shipping, plus there was a promo code for $15-off (EMCYRYT32) so the drive shipped was only $64.95 and that was simply too good to pass on.