It's probably an older attitude, but I still peg 3 years as being a reasonable expectation for electronic equipment to last for, whether that be home entertainment, phones or computers.

I was late to the iPhone party, and started with a 3GS just over 2 years ago. In December 2011, I picked up a 4s, this was because the contract on the 3GS was about to run out, and the carrier was closing down. Getting a new phone was icing on the cake.

It irks me that a new product is pushed out every year, but it looks like I'll be on an upgrade path that lasts at least 2 years.

I bought an iPad 2 for my wife, for Christmas. Again, a late starter, but I'll want to be sticking to a 3 year cycle for that.