Excel is one of those tools that people use and then find out "damn, it can do that, too?", so they have to adjust their ratings of their knowledge. lol. I doubt most people use even 20% of what it's capable of - I know I don't.
Used to be 8/10 Now probably 6/10 I've wrote macros in excel that used VBA to open up another program (SAS), run something using that program, and then populate Excel with the output. I now don't even know where to start in doing something like that again but I still mess with pivot tables and simple Excel Macros
Probably a 4/10. I'm pretty bad with it without having to Google. Other Microsoft products like Exchange are a different story to me though.