I was born in here (in Cambs) and currently live here on the flattest part our our wonderful blue planet .Mountain biking in Cambridge ? a bit like kayaking in the bath with no water but dont let that put you off.
I also live near Addenbrookes, and a student there and theres a lot of nice road riding to be had going around the villages. Some bridal way riding starting near Addenbrookes about a mile or two away that can take you past Linton, but its VERY straight and some other lesser know tracks around (some nice pub stops on the way though)
Pubs ? Mill Road and the pubs down the side streets are a good bet, cosmopolitan and nice atmosphere in most. I second what someone else has said about bikes and Cambridge....nice bikes never last long here !. I say this experience having had either bikes stolen (whilst being locked up like fort knox) or having front mechs cut off or various other bits taken. Best bet is as Willard says get a 'pub bike' which draws no attention to itself.
This also goes for Addenbrookes Hospital which over the years has been a hotspot for bikes being taken or bits disappearing although they do now have a 'secure' bike area, how secure is debatable since collegues have told me how easy it is to gain entry to the secured area.
All in all a nice enough place to live with easily identifiable sub groups when over hearing pub conversation
Group One - Overhearing conversations about Cambridge United, usually a local who will reminisce about the days of John Beck
Group Two - Overhearing conversations about Cambridge City, a true local, balanced by the fact they are supported by only 3 people in Cambridge............make that the planet
Group Three - Overhearing conversation about particle physics/D.N.A, Cambridge University lecturer with huge head to house the massive brain they have to carry around
Group Four - Overhearing conversation about political science, Cambridge University student, usually with rugby shirt, collars turned up and probably called Rupert or Tarquin
Group Five - Overhearing conversation with strange accents from fellow of a diminutive stature, usually from Newmarket and probably jockeys
Group Six - Overhearing conversations with strange accents from large gentlemen who look rather rustic, definitely farmers
Group Seven - Overhearing conversation from group in multiple languages, almost certainly students from Anglia Ruskin University (dead cert if its in CB2, some pubs in town or off Mill Rd). 'The Other University in Cambs' which has comically placed a sign at the train station to establish and remind people that there is another Uni in Cambridge.
Group Eight - No conversation from group until the 5th pint at which point conversation is loud enough to heard from Ely, staff night out from Addenbrookes Hospital
Group Nine - Computerised voice from group but no discernible source, Stephen Hawking, who can only wish he went to Anglia Ruskin University and not the world famous, ground breaking Cambridge University
Hope that helps