Avantages
Drawing points for Bloomberg: great compensation/packages, intelligent co-workers, industry leader. At work you'll be working with some very intelligent people, some known widely throughout the industry. It's also nice to work for a company that is the industry leader in financial data and news - it blows all competitors out of the window. Depending on your personality, you may or may not like the fact that the pace at Bloomberg is very fast. Unlike traditional software companies, where time is spent on requirements gathering and design, Bloomberg emphasizes time to market and getting things out the door: software moves once a week, not once a year like other companies.
Inconvénients
The technology is ancient (the majority). A lot of programmers are simply maintaining legacy code (fortran, c) that cannot be retired or converted. The company also uses a TON of proprietary software, all developed in-house. For example, they've created their own Service oriented architecture (ala WSDL), two home-grown databases, entire UI framework, and other things. It's very easy to get "stuck" at bloomberg because you might be using proprietary tools 75-90% of your day! Also, there is an entire lack of structure when it comes to the software development cycle. Projects are handed out with no formal written documentation: let me repeat, NO formal written specs! There is also NO official testing (no qa teams whatsoever!). The programmer is expected to perform the testing of their applications.