Pros
UBS provides good benefits if you want a 9 to 5 job for life with little pressure to perform. Benefits are reasonable - good holidays and depending on rank you get additional personal days off. Work/life balance is probably the best reason to work at UBS and the longer you work there the more perks you get. If you're not really interested in pushing the hours you can hide out in middle management and survive on mediocre performance. People are generally nice and friendly though needless to say if you want to climb the food chain then your performance must increase.
Cons
Too many 9 to 5'ers and generally loose tolerances for performance - it's rare to see someone reprimanded for poor performance which impacts your team. The result of this is a culture of 'it will do' tends to permeate throughout the firm and it's easy to become a slacker which over time will take the edge off your performance (that's Ok if you want to be a lifer at UBS). Back office is exactly that - back office, or better put basement office and is generally focused on expense reduction so don't count on expensing pizza for the team if you're working late or getting a decent cut of the bonus pie.