The case study isn't your basic strategy, market expansion case study. They give you a bunch of information about a firm in terms of their future vision and how the company works at the moment, i.e. their operations. They'll usually have an issue where some department wants to introduce a new technology and you'll have to decide the whether it's a good idea and have people related issues etc.
The case study tends to be the same every year (i had the same one for 2 years running).
There are 8 questions at the back, make sure you have something to say about all of them. Some of them don't require the case study material and are just general common sense. The last few questions generally require performing calculations.
It's not a disaster if you don't get through to the end as there's quite a lot to do in 25 minutes, but if you haven't done the calculations they'll ask you an overview of how you would go about answering the question, i.e. what are the calculations you would do.
Make sure in your answer, you consider all aspects of a business, not just the mainstream ideas that are given in the case.
For example, if you have to perform cost calucations, remember that cost is not the only consideration businesses use to make a decision, think of some issues that don't involve figures.
Good idea to read the questions at the back before the case material.
As for the competency interview, it's really quite basic. 'give me a time when......'
They ask you career motivation questions quite thoroughly so make sure you have good solid reasons as to why you chose deloitte and why this practise area. It's always great if you can come up with reasons that differ from the norm and base it on features of the specific programme.