All depends on how you take care of your phones or electronics in general. I've seen some that just don't care about their electronics. I shake my head at wanna be photographers throw their expensive DSLRs into a large purse or unpadded backpacks But of course, being a techie, we shake our heads at a lot of non technical people abusing their electronics. The Infuse is too new to see how long it will last under normal/heavy usage. The nice thing is you don't have to worry about battery problems (if you have any) and just buy a new replacement. Unlike the iPhone and having to send it in. My Infuse is humming along with no issues for about 2 months now. And that's stock rom but rooted. I'm awaiting for official AT&T gingerbread update so the wonderful XDA dev's have something stable.
It comes with a 1 yr hardware warrenty from samsung...so it you get a new phone at close to the end of the first yr and the second phone last a yr..then your 2 yr contract will be up and time to get a new phone.