Pros
JPMorgan Chase is a "target-rich" environment for technologists -- there's always something to fix, or something to break and then fix again. The benefits are good, the pay is very good, the Columbus facilities are nice, and they have a lot of money to throw at shiny new toys. Some programmers and engineers have more stressful lives than others, but there is nothing like the horror stories one hears from game development shops. You can come across the occasional diamond in the rough or guru while working there, and it is a good place to network for future job prospects.
Cons
JPMorgan Chase is not a technology company. There is little respect for technical analysis or input. Management often overrules or ignores the actions of the technical staff, and there is almost never any effective recourse. There is little room for advancement for someone not interested in management or finance. As a multinational bank, JPMorgan Chase must be one of the largest users of technology in the world -- yet as a rule, they give their janitors and their engineers roughly equal influence over the direction of IT. Design by bullet point is a pervasive practice at JPMorgan Chase, since half of the people there are apparently functional illiterates. Death march projects are common. Often projects exist or proceed the way that they do solely to perpetuate various middle management fiefdoms.