I go swimming nearly everyday (started this about 2 years ago) and feel so much better for it, definatly helped me tone up my hip, thighs and buttocks, and my upper body to, did nothing for my belly though :(
the only problem with our pool is getting the timing right for when its quiet!
We have three lanes (slow, medium and fast) not everybody swims at the same speed and if people were a bit more courteous, If someone is faster than me then i always let them pass, or if someone lets me pass then i make sure i say thank you! (moan over)