Pros
ARM has an open culture that is very refreshing if you've been in an organization like Intel where it is hard to get hold of the information you need to do your job. It is justly proud of what it has achieved from humble beginnings. Cambridge, as well as being a beautiful city to live in, is a place where almost everybody is intelligent, and ARM only takes the best, so you will be working with exciting people. For experienced staff, ARM pays well and offers a range of bonuses, in particular a substantial new starter bonus which you will get at the end of your first year at ARM. The takeover by Softbank has not affected the culture, all that has happened is that our horizons have been widened by the opportunities for new investment.
Cons
Don't be starstruck by being offered a position at such a great company - make sure that the position is one you really want. If you are an experienced individual and want to keep your technical skills going, make sure that this is not a management position that you are being offered.