Not too bad. Unless you're running virtualisation, etc.
I can't answer that. But I've tried playing 2-year-old games on 8400M/9400M and found it barely playable.
Very simple to install. Virtualisation is not a panacea though, and intensive computational needs will make the machine wind up much more than a dual boot scenario. Boot Camp is also not a 100% Windows compatible environment so be prepared to see more BSOD's than you would on a 'genuine' PC.
3.5 hours. Not class leading by a long way, but not terrible. I wonder where people fish 5 hours out from. Oh yeah, Apple marketing. Because everyone believes that, right?
I have it installed on all my Macs, but Office for Mac pales in comparison to Windows versions especially if you actually do more than slightly scratch the Office featureset. Excel in particular is useless to me. As light-use programs I prefer the iWork suite, but for actually documenting, numerical work, etc I need Office - and not the Mac version.
How many years did you get out of the PC? It's the same time. There's no magical lief extension with a Mac - if you outgrew your old PC in 3 years, the chances are that you will outgrow the Mac in another 3. The only major difference is if you actually don't know how to choose the best machine for you: In which case, Apple's severely limited lineup effectively forces you to overbuy in most cases, thus curtailing what the vast majority of people who don't know anything about computers do, which is to buy something which is too cheap when given the choice. The overbuying can be thought of a life extension for people who aren't capable of making an informed choice.
No. I use reliable machines - currently notebook wise, the Sony SZ700-series and the Dell Precision M6400 Covet runs some of my analytical suites, visualisation and design.
Nothing in general from me.