Plymouth uni's socail facilities are somewhat limited in my experience. the student union is quite large but desinged for nights out so doesn't have a great atmosphere during the day. There are loads of uni cafe's on campus though so if you are wondering where to go for lunch with your friends (or alone) you are never far from a catering outlet! The SU shop is something I didn't go into for a while but they sell a good range of lunch food, snacks, stationary etc and its really handing having it on camous, right opposite the libray.
Talking of the library, its a really great place, everyone there studies hard in the quiet work rooms so you know you can work done there and everyone is really friendly towards each other. People regurarly ask starngers to watch their laptop for tem while they head of the buy a snack!
Overall, I would say te uni's socail facilities and sapces are limited, but its what you make of them!