If you are really looking at using more than a handful of nested If's I would recomend you think about alternative ways of defining and tackling your problem.
There is nothing wrong with using complex If's it is just that getting them correct and maintenance of them is so much more difficult.
Options like Choose or writing a UDF may be a simpler method.
Instead of using If's to find the positive, can you use less if's to find the negatives.