My 14-day is tomorrow and I'm keeping it. Like most on here, I was torn between the Sport and the SS. Unlike most, however, I opted for the Sport. Even though the weigh difference is not huge, I did feel that the Sport had a near weightless feel to it. I even forgot I was wearing it when I did the try-on session. The SS was still very comfortable, but I could tell I was wearing it just like I can with my SS traditional watch. That is another reason I chose the Sport - I wanted to save my SS watch for nicer occasions and not be tempted to wear my Apple watch. I did end up buying the black leather loop strap to go with my silver Sport watch, as I found that was enough of a compromise to help the watch look nice and I could wear it business casual. The final reason was really the price. Since it's a first generation device, I imagine I will be very tempted to upgrade in a few years. And knowing I shelled out $200 less for a device that will be thrown in a drawer with my old iPhones made me feel a little better. Next round I very well may go SS though.
As far as why I'm keeping it, I find I utilize it a lot more than I thought I would. Initially, I thought it would be good for mostly just the notifications. And the notifications are great. I really like how it just taps you, almost like it's saying "hey, I got something for you" rather than just a noise from my pocket or from across the room. I use a lot of the other features, too. The alarm and stopwatch are very convenient, especially for how much I cook in the kitchen. I also take my dog to the beach a lot, so I have a Tide app that has Glances, so can easily see when it's high or low tide. I follow our Turnpike Authority on Twitter and get push notifications from them - they only tweet when there is an accident somewhere, so it's really nice to get that notification on my watch since I drive for a living. Messages are a mixed bag of useful. I have a few quick replies in there, but they are usually only useful for my wife ("see you soon," "heading home," "thoughts on dinner," etc). The only thing that is frustrating is having to scrap a whole message if dictation gets one word wrong. It gets it right 75% of the time, but of the other times it's kind of a pain and sometimes I just end up pulling my phone out anyway to send a reply.
All in all though I think the benefits of all it has to offer far out weighs returning it. I would definitely miss it now that I have been using it for a few weeks.