The problem I have had with tabs is that some editors will convert tabs to spaces when you edit a line but on the lines you have not edited they are left alone. This of course looks fine in your editor. Then someone else loads the file into their editor where they define tabs differently and the code looks bad. So they reformat.
You can see where this is going :)
Diffs are 99% whitespace changes and then some easy to overlook real change. Code review becomes impossible.
We have only one coding standard where I work "Indentation is 2 spaces"
