I started on 64 bit pretty soon as it came out (I think). My experience level caused me all sorts of problems getting extra software working in 64bit. I also believe though this may have changed that I couldn't use apt/synaptic with 64bit at that time.
I abandoned 64bit and have learnt quite a lot since, osmetime soon I will jump back to 64bit OS - after all thats what a 64bit processor is for
p.s I thnik the amd64 is a cracking processor, workes effortlessly, runs pretty cool, and the prices seem to have dropped a bit since I bought in, the motherboard support is supposed to be much better now as well.