Today's time trial was different in more ways than one to the opening time trial on stage one. This was a long time trial compared to the comparative shortness of stage 1. The time trial was up and down today compared to the virtually pan flat stage one, and Jan Ullrich didn't suffer a crushing defeat. However, of course there were some similarities - it required a huge effort by the riders, the riders used lots of aerodynamic equipment, and Michael Rasmussen put in another poor time trial performance (albeit, one hundred places better than the opening stage).
Whether it's a short time trial or a long one (assuming a TT is more than about 90-secs in duration) the limiting factors are very similar: sustainable power output. Of course, it's not just about power output, there are other factors as well: body shape, size and your position, bicycle equipment, body mass (in a hilly TT), bike handling skills and pacing skills.
We saw that Michael Rasmussen lacked some skills today, as well, as the raw power required to time trial at the highest level. Not only did he crash once due to poor handling skills on a descent, but it's possible that his first crash (note: I'm speculating. I do this a lot!) was due to anxiety. As Michael would have known he was under direct pressure from Jan, it's certainly possible that he started in a very anxious state. This would have meant he was possibly not in control - he was riding beyond either his physical limits at the early roundabout or his skill level (as he may have felt he would lose time in the corners) and this led to early demise.
Once you've experienced a crash under these circumstances it can be hard to rein your thoughts in and negative self-talk can cause further issues as panic sets in. If you do experience an episode like this, it can be crucial to take a second and a few deep breaths (even if that means coasting for a few seconds) and realign your thoughts and start to concentrate on what you need to do rather than worrying about other people (which is out of your control). For example, this could be thinking positive thoughts about pedalling smoothly or maintaining a specific power output or heart rate zone and then zoning in to your effort.
On a technical circuit such as stage 20, which twists and turns, and climbs and descends, it's especially important to pre ride the circuit and to make mental note of which lines you should take through a corner, or at what speed you can take a corner at. Ideally, you should also note road surfaces, areas where you may be exposed to winds, and how steep the climbs and descents are.
If you reconnoitre the circuit with plenty of time (as I suspect Lance and Jan did) you can then mentally play the circuit over in your head. This will allow you to 'practice' the corners and other difficult areas so that you know where to brake or accelerate, etc. We can see that several riders over-cooked a very sharp hairpin corner including Ivan Basso. This may have dented his confidence for later in the race.
Another skill that a good time triallist should possess is the ability to pace a course correctly. That is, they do not 'blow' before the finish. You should aim to arrive at the finish having exhausted yourself. This involves two aspects of TTing: learning how to do as much work as possible, and pacing the hills, the descents and the flats to the best of your ability.
In a flat time trial you should you should aim to ride at an even effort trying to maintain a constant power output at an effort you know you can just hold for the duration of the event. On a circuit like stage 20, or where there's variable winds it can pay dividends to ride at a varying intensity - higher than average TT power on the hills and into headwinds, and below average on descents. The exact intensity that you ride at will depend on many factors including your fitness, and ability to push past your average TT power and the exact topography of the course.