There have been other threads on this recently, danieq.
Apparently, 'layering' is a term often used when people start off with one product such as bath oil/shower stuff, then follow with another product of the same fragrance, but these days I tend to use it for stuff like starting off with an oil, then adding another or spraying something after applying an oil (but not actually on the same place!).
It works with oud/rose, etc., and I was recently pleased when I sprayed a newer, weaker version of something after using the oil-based 'Ancient Resins', which is frankincense-based.
I've never tried doing this with two sprays 'though - others should know more, although it could be wasteful if done with the more special fragrances!
If it's awful, you can wash it off ;)