I alternate between my collection of Sufferfest Vids (I have 6 of them) on my fluid trainer and a spin session on my rollers (45min - 1 hr max).

Did revolver today: http://connect.garmin.com/activity/155445180

I'm more of a masher than a spinner - much more comfortable at 90'ish cadence. Anything over 100 is an big effort for me.