One thing to beware of is that you will not automatically be expected to want to claim PIP - you have to tell them you want to claim it, even if you are on DLA already. Don't do that until you get your letter - otherwise they will put you through this process sooner than you might need to. The first part of a claim is just to register and go through some very basic entitlement questions (e.g. that you live in the UK and have done for the required period), and then they send you a form to complete where you get the chance to 'tell your story' (I love the language they use, it makes it sound so friendly) at which point you should make sure you get help from a welfare rights adviser to give yourself the best chance of success.
We will not know the final rules for assessment until this October, when the Regulations will be put before Parliament. This will give us the scoring system. But the rules will certainly be harsher than for DLA. There will be two components that are similar to the 'mobility/care' division for DLA, but for PIP they will be called 'mobility/daily living'. Each of those components will be split into two rates, either standard or enhanced. You will need to score 8 points to get the standard rate, and 12 points to get the enhanced rate of either component.
DLA will still exist for under 16's. Also people over 65 will keep it if they already have it and remain entitled. Anyone over 65 wanting to put in a new claim will still have to claim Attendance Allowance. People will still be able to get Carer's Allowance if the person they look after gets the daily living component (at any rate) of PIP, and PIP will also remain a passport to a Blue Badge for anyone who gets the enhanced mobility component.