I use the training block because it's annoying to ride without one and be tilted downwards. I tend to agree that unless you're jacking your bike up a LOT, the positional differences are near-meaningless compared to the actual power/work you put out on the trainer which can be done regardless of position.

I've got the CycleOps climbing block with multiple heights, and I just ignore the heights and use the level one - I wasn't getting any more climbing benefit from the inclined ones.

And while you can just use a block of wood, phone book, etc to prop up your bike, I found all the solutions wanting, as I use my trainer a fair amount. The big CycleOps block is very stable, which is useful when doing a lot of hard riding on the trainer. (Damn you SPinervals!)