Re:
Lovely job, it makes no economical sense, but a lovely job none the less.
Regarding the brakes, most mountain bikes have bosses to fit either cantilever brakes, like this:
Or on later rim braked frames, V-brakes, like this:
Because of the short distance between the pivot and the brake shoe the set-up is fairly rigid and when well set up they have very positive action with plenty of stopping power.
Calliper brakes, like yours, are more commonly found on road bikes. On a road bike the narrower tyres mean that the whole calliper can be very compact and the arms of the calliper relatively short, compact and rigid. Modern dual pivot calliper brakes are a big improvement on the earlier single pivot brakes, like yours, and have a very positive feel with plenty of stopping power.
However, on an MTB with fat tyres, the whole calliper has to be a lot bigger with longer arms to fit around the tyres and reach the rims, which means that there is a lot more distance between the brake shoe and the pivot, which means there's more flex and the brakes feel less positive and ultimately less powerful as some of the power is wasted flexing the brake arms rather than pressing the shoes to the wheel rims.
You can get some better long reach calliper brakes that should be an improvement on the ones you have, but would in all likelihood still lose out to well set up cantilever or V-brakes:
http://www.wiggle.co.uk/tektro-r559-ext ... liper-set/
Having said all that, if you're happy with what you have and they're doing the job I wouldn't worry too much. It's easy to forget that you get spoilt. I was perfectly happy with the dreadful single pivot calliper brakes on my road bike, it was only after I had a mountain bike with cantilever brakes that I had a comparison and realised how bad they were. :?