Pros
It's possible to commute from North London to most GSK R&D sites, so you don't have to live somewhere miserable, like in other big pharma R&D departments. Some members of staff are keen to encourage cross-departmental knowledge sharing and collaboration, and there is an internal network to facilitate this. Also lab books were kept electronically, online, and were visible to others. During my internship I was given the freedom to create my own project. I also worked in a group that maintained good links with academia. Some fellow interns even published their projects. Apparently lots of scope to go part time later.
Cons
Regular reorganization leaves some departments feeling empty. The pay doesn't compare to other big pharma R&D departments, and it's expensive to live in north London. There's no atmosphere outside of regular working hours as no one seems to feel the need to work overtime.