In the days of Vista, A LOT of users were not happy about the experience yet still wanted DX10 Gaming and decent OS performance, so a movement started that introduced Windows Workstation 2008. You see the kernel was infact quicker in the server product, real world tests prove as much as 15-17% quicker.
Besides this, if you're a developer its often great to work directly on a server product, but at the same time you want to still keep your after hours activities (gaming, movie watching, etc) Your first answer is YES, all of these can be done on a server.
You will run into some practicality issues, but most of these can be overcome. For example - Certain AV products won't install on a server. But I've always found a workaround for this. Another thing is some Nokia phone software also required some extra hacking to get working, and at one stage even Windows Live Products needed to be "hacked" to be installable on a server product. Some old games that check for OS, also might not install on a server OS. Perhaps the biggest loss, Windows Media Center.
However the reverse is true, most server products can be "tweaked" to get to work on client systems. Take SharePoint for example - you can get that running on Windows 7, if you know what you're doing.
I am not sure if you're going to see any real performance increase in using Windows 2008 Server R2 vs Windows 7. Windows 7 sports a very well written kernel and explorer shell, and I have yet to find any convincing evidence that the server product is somehow quicker.
I guess its all about preference and experimentation, don't let anyone on here tell you otherwise. Do what you want, and enjoy the experience!
If you want some inspiration I would suggest looking at this web site: http://www.win2008workstation.com/
Enjoy and take care....