I use Fluid (http://fluidapp.com) for a similar purpose as Nativfier... it's because my brain is hard-wired from years of use to equate Cmd-Tab (or Alt-Tab) with "task switch." My brain thinks of e-mail as a separate thing from my work (editor and browser), and I personally don't like conflating my browser with different tasks like e-mail.

I know I could just learn Ctrl-Tab or Alt-{ or whatever to cycle through dozens of tabs, but Cmd-Tab works for me. Different strokes for different folks.

I'll probably check Nativfier out because Fluid hasn't been updated significantly in a while and uses an old renderer, and it's a bit laggy w/ HuBoard (the front-end to GitHub issues that we use at work - it's pretty JS-intensive)

IMO for web apps that you have open all the time (maybe Asana, Google Docs), native OS navigation and window management is significantly better than tab navigation. Of course it doesn't have as much of a benefit if you do it for every tab you have open.