I got an iPhone 4s in August. It is one of the best things I have ever owned (1st IPhone). I have owned other smartphones but this is awesome. (I know other up to date smart phones are just as good but I have never owned them so cant comment).
The phone itself is not waterproof and seems very delicate, but I bought a 'Lifeproof' case for it which did cost £50, and is 100% waterproof (allegedly and so far is) and will protect the phone for the next 2 years until I upgrade, and hopefully sell the phone for a reasonable amount.
Within a few days of owning it I did manage to drop it in to the quench bucket in my workshop ! Boy am I glad I bought the case ! I have since dropped it once on concrete, it landed on the corner, but there is no mark to the case and the phone works fine.
I bought the case from Outdoor GB
http://www.outdoorgb.com/p/LifeProof_iPhone_4_Case/ which were the cheapeast at the time. There are copies on ebay for less than £20, but I don't know if they are 100% waterproof.
Battery wise the iphone lasts well in day to day use, I have the Landranger Gps app on the phone, and the first time I used the app, the phone was fully charged & I did a 10.5 mile walk with the gps on all the time, and when I got home the battery was on 52 %. I have since bought an external battery backup just in case.