I did it this year on a hardtail TSW and the only time I saw the leaders was at the presentation each night, but that's what I expected anyway. As with all events you're often amongst your own peer group and you get support and encouragement along the way. You do need fitness, and my training was a daily 15mile round trip to work and regular fell runs up to 10-12 miles but with more of an emphasis on two or three hour bike rides as the TW got closer. The most important thing in the actual event was the willingness to accept that much of every day would be hard, uncomfortable and sometimes just bloody painful. There's a steady weariness that creeps in over the first four days as your body learns to cope with the demands being made of it, and that requires a certain level of determination to overcome. The days consist of pretty much the same routine, up early, fill yourself full of stodge, pack your tent, get on your bloody bike and ride. Then, hours later, wash your bike down, clean yourself, stuff yourself with more stodge, get to bed about 9 o-clockish and try to sleep and do it all again the next day, for ever and ever. What's it like? effing brilliant. the sense of achievement is still there. And you get a pretty good finishers jersey and a very limited edition buff (I wore mine at the OMM two weeks ago although nobody recognised it!....b***ards)
The TW is the hardest, and best, event I've ever done. I couldn't recommend it more highly. Do it.