Does it taste like pound cake??
From what I've read Madeira cake can range from rich sponge cake to poundcake (depending on the recipe).
Here's a traditional pound cake style Madeira cake recipe by Nigella Lawson:
Sponge cake style Madeira cake recipe:
We use maderia here a lot, I don't use it for cakes, although it is heavier than a sponge it is still not heavy enough to put fondant on etc. Would be ok for buttercream, though.
It is indeed a cross between a pound cake and a sponge. Much better than a sponge (personally I hate sponges, they are so tasteless, then when you put icing on it all you taste is the icing YUK!) and lighter than a pound cake. Hope this helps, if you need a recipe for this please let me know have a few differing ones you might like to try. Cheers
Re finding out what it is like - perhaps you could try making one and see how you get on with it.
I use Madeira for some cakes and find that covering them first with marzipan or almond paste makes a firm base on which to put sugar paste.
Anyway, why not make one and see if you like it and can use.