If you have the time, the best thing about TRAINZ is you will run out of time before it runs out of options. No model railway problems of "no space left in the spare room"
A few years ago I started our local area in real scale using Ordinace Survey maps and phots etc. Ended up with a route streaching from Birmingham to Tamworth and (nearly) Nuneaton. Unfortunatly that was back in UTC and I haven't found out how to transfer it into 2006 yet, any suggestions anyone (please :'( !!!!)
you can just do what you want when you want and it can be really satisfying to adapt bits and bobs from the DLS to end up with some scenic item of other that looks like what you know the real one looks like.
The only problems I came across are:
1. The bigger it gets the harder it is to keep up with the landscape.
2. Some scenic items (houses etc) are not really in scale so don't "fill" areas as they should.
3. Urban areas need careful thought as they can bugger up frame rates when running the sim.
4. SAVE, SAVE and SAVE again. Big routes crash more easily (boohoo)
GO FOR IT CHIEF!