Pros
People are intelligent (professionally), slow-performers are weeded out of the company, there are many learning opportunities, the size of the firm gives you the flexibility to work on projects that interest you. This is basically a great company to list on your resume. For the most part, it adds credibility.
Cons
1) Company culture & 2) work/life balance: 1. Company culture is rather "cultish". There is a huge emphasis on "building your personal brand" (marketing yourself like you are some kind of product), "eminence building" (being a leader in a particular field - this involves working later hours and writing white papers that no one really reads), and over emphasis on the symbolism of the "green dot" (the little green dot next to the Deloitte logo somehow represents the depth of Deloitte's intellectual resources. These three concepts, among others, are alluded to so frequently by senior management in company e-mails and meetings, it's scary. 2. In addition to client work (your real job), the only way to get promoted is to participate and lead various extracurricular activities, particularly community service or activity groups within Deloitte. The current expectation as of 2012 is that you do 200 hours a year of this stuff on top of your real job. If you fail to meet this requirement, you will not get the highest rating. So basically, if you work for Deloitte, you have to do two jobs well. Additionally, don't be fooled by the generous vacation package. It is practically impossible to take all your vacation and meet this metric called utilization (the amount of time you are billing the client/divided by the time your are employed assuming a 40/hr work week) at the same time. If you stay several years you will watch the vacation you accumulated over previous years disappear and probably not even be upset about it because it is the norm.