My Windows Phone Fear

I am in the market for my 2 year upgrade (Verizon) and Windows Phone 8 looks to be exactly what I want in a phone. I have one big fear of changing from my Iphone 4s to windows phone (probably the Verizon variant of the 920).

Durability...

Now it is not so much the hardware I am worried about as Nokia is well know to make great durable hardware. What I am worried about is does the phone continue to run like day one. Before my Iphone I had a Palm something or other and then a BlackBerry Bold. Both of these devices deteriorated so fast on Battery life and lag within the OS that they became unusable. Luckily an upgrade came during the right time and I was able to get an Iphone 4S.

So my question to you guys is has your Windows Phone shown signs of slow down. Reduced Battery life? Lag on transitions? With my Iphone it still runs like day one and that is one of the few things I really like about it. I am hoping Windows Phone is the same as I only buy a new phone every 2 years.