Pros
Reasonable benefits price/value Somewhat flexible start time and end time Helpful coworkers Work (as a vendor) for big successful companies (such as MSFT) Learn about some aspects of big successful company's business that can help you gain experience Access to Vendor cafeterias for lunch (if you are part of a specific project) Paid holidays if you work full time Contract with Vendors may be 6 months, so there is some job security.
Cons
Work environment for in-house vendors is not what I expected. Many workers eat at their desk and do not take breaks. Workers hours/minutes per task are measured way more closely that needed. It is possible that the only way to get your 8 hours per day is to work through your breaks. Pay is very low for the level of work that you are doing, and basically no raises. This is probably because they figure they can get someone to do the job (if they did not hire you). And they know that there is some "draw" for workers who are willing to work for low salary if they know they are working as a vendor for a large IT company. No guarantee that you will keep your job even if you are full time. You could be laid off at any time, and especially if the Vendor does not renew their contract with Pactera.