Pros
Salary relatively high. Opportunity to work on various parts of the core business such as anti-phishing, security scanning etc. Friendly staff and atmosphere. Free lunch. Relaxed working hours (turn up late and leave late is fine). Ability to work from home when you need to. Opportunity to work weekends from home and earn holiday time. Pick and choose at what problems you would like to tackle. There's never nothing to do. Relaxed work schedule which concentrates on gradual improvement of systems.
Cons
A lot of Perl which can be painful at times. A lot of old technology still in use, but improving. Management can be short-sighted by blocking innovative solutions and instead favouring short term modifications on code in need of refactoring (I see why this is necessary in many cases from a business point of view but I believe it harmed morale). Took on too many staff at one time. Further employment offers based on good word of who you happened to be working with and not technical or personal aptitude.