Pros
Great people to work with. Strong company with great job security (no layoffs, if they need to eliminate positions they reassign people to different groups). Managers work to maintain a really good work/life balance.
Cons
Difficult to progress in the company. Pay is well below the market average, especially considering the level of candidates that are being sought after. Due to this, there is high turnover which makes work within project teams stressful (same work for fewer people). There isn't enough emphasis put on expanding pertinent job skills. Upper management has a very outdated approach to SW development. Rather than invest in the company/employees ability to enhance and overhaul products, Paychex goes out and purchases companies and products and then just maintains those. They don't create their own applications... or even make major upgrades and enhancements to what they have.