Someone mentioned fractional reserve banking... although it could exist with bitcoins, I don't see the same advantages. While I need a bank to protect my $millions (I wish) and make transactions for me, I could do that myself with bitcoins. I also don't need interest to maintain my wealth as bitcoins are inherently deflationary. Actually my biggest concern with bitcoins is the incentive to hoard instead of spend or invest. You might not see that as a problem but it hasn't ever been tried AFAIK so it's a leap of faith at least.
I'll assume for a moment that there will be bitcoin banks and such.
I think it is a misconception that bitcoin is inherently deflationary. it very much depends.
with bitcoin only the base money supply is constant eventually. that is less inflationary than all other fiat currencies, but it doesnt mean there is no inflation. there can be, when banks do what banks do: create money by creating credit.
see the money supply definitions M1-M3.
even if bitcoin is the currency I doubt bitcoin will be the method of payment of the end-user, more like the back-end of banks and some enthusiasts. so banks basically do what they do now, except their refinancing would be vastly different because there is no central bank, which is the most interesting part of bitcoin and a huge difference.
but besides that I don't think that much would change.