It's not nearly as fast, by at least an order of magnitude. Also, because there is no centralized location for apps to be stored (e.g. /Applications) it has a harder time succeeding as an app launcher.
I can't tell the difference in speed between a 2007 Lenovo T61 and a 2010 MBP.
Works fine for apps. Windows 8 actually makes distinction between documents, apps and settings.
It never worked well for me, but I kill my search indexer process a lot because it turns my fan on.