I have always used methi leaf in my Madras, only because nearly every madras recipe I have seen uses it.
On Friday I made a Madras and omitted the methi, and I have to say it was a fantastic curry, better than normal. This could be down to other factors though - The jb base, cooking the ingredients in a different order or the omission of methi.
I wont really know till I have tried it a few more times, but it definitely hit all the right notes.