I live near Pompey and don't be worried about the sailors. My brother in law is in the Navy there and a lot of them (including the girls) are quite hot!
However you have to be careful if you go out clubbing in Southsea, there has been a LOT of violence there so I don't advise wandering about.
The shops are great, but don't go to their McDonalds because it's the worst in hants. Gunwharf Quays is fantastic for cheap designer gear and the cinema is good as well.
Around Portsmouth you've got a lot, you have Fratton with the football stadium, as well as some cool alternative shops. You've got Southsea with a slightly more relaxed shopping atmosphere and then you have Commercial Road which has any shop you can imagine. My favourite is Withit! Plus someone always puts washing up lidquid in the fountain. If you want fancy dress clothes go to U-Need-Us. You can get nearly anything there.
The place has 3 good places for gigs, The Wedgewood Rooms (The Wedge), The Guildhall (Aka Skater Central) and the Pyramids (Fantastic swimming pool). A lot of great bands play there and it's very easy to get round the back and meet them.
There are a load of pubs too, my favourite being the Registry and Walkabout.
A lot of my friends have gone to Portsmouth Uni' and they are really enjoying it.
You can wake up on Saturday morning and think "hmm what shall I do today?" and jump on the hovercraft and go to the Isle of Wight.
Hope this helps