Hi there

I'm still getting my head around the workings of this concept. But from what I've been able to comprehend so far there's a lot of game changing concepts that have kept me hooked.

I'm guessing this is part of the process:
As a node attempting to create a block, I would pick the last block from the longest valid chain. I'd then gather up all the information needed for the new block and start sweeping through the nonces until I get my leading zero hashes and I'd announce the block and collect my 50.

I had a few concerns about the process (probably because I haven't figured the whole process out):
If new transactions got announced while I'm solving my block, I'd have to gather information about these transactions and start sweeping again from the beginning. Doesn't this make it favourable for a miner to ignore transactions so that they have a better chance of solving the block? (I assume that there is a solution available for every node, only at different sweeps?)

How exactly do all the nodes agree on the difficulty of the solution? ( I assume the number of leading zeros is the difficulty. Wouldn't this make the difficulty double or half rather than a more granular step?)

On a separate topic, I read about MTGox rolling back??? Is this their own data rather than the bitcoin network? Did MTGox acquire some bitcoins at a cheap price to facilitate this rollback?

Sorry if they are dumb questions. Atleast I posted in the newbies section

K