My contribution to the tabs vs spaces war. It's very silly to use spaces, but when you contribute to open source you have to do it, so here's how I cope:
Tabs for indentation by default, but when you open a new file press <Leader><Space> to highlight lines indented with spaces. If you see red everywhere, it's a space indented file. <Leader><Tab> switches to space indentation, and <Leader>j<Space><Number><cr> sets the number of spaces per indent.