WOW...donno how I missed this thread. I too have a swimming pool at home, but I'm also a runner. Just started a thread about this topic actually. I have a 20 x 40 free form pool. I haven't been counting the laps, but I usually swim about 1-2 hours 1-2 times per day. I'm a fish...and it's been really hot here in the South (where I live), so I've been living in the water.
To answer your question OP, I'm not sure how well you lose weight while swimming since I'm in maintenance, but I can tell you that I've stopped running for 2 weeks now, and increased my food intake (adding more goodies) and haven't gained a pound. So far so good.
It's just hard for me to feel like I'm really "working out" since I don't sweat while swimming and my heartrate never climbs like it does when I'm running 5 miles.
Anyone else feel like this. Are you suppossed to be exhausted after swimming for an hour?