If you can use a garmin or other bike computer and constantly monitor all the data such as speed, cadence, HR, it really helps pass the time (aswell as using music or tv). Intervals of some description (they don't have to be maxed out ones) also help because it gives you something to focus on. The most "boring" sessions are probably recovery spins where you are lightly spinning in zone 1 HR for a prolonged period! All the guys I know who train for TT's are using the turbo all week and maybe getting out once or twice on the road for "base" miles, around 35 - 40 mile rides @ approx 17 - 18 mph.
I find the turbo doesn't replicate the real world road rides, and why would it, there's no wind no gradients etc. My HR can stay relatively low on a turbo unless I max out, where as on the road it is far higher. Which is why most believe you should mix turbos with the occasional road ride if you can.