I have done pleats a few times, including on my own wedding cake (link to pic below). From the comments I'm not sure if everyone is picturing the same kind of pleats. The ones I picture are pleats like a skirting attached from the top edge of the cake and left to "drape" on the cake board.http://cakecentral.com/gallery/1133953/
Using 50/50 fondant is a good suggestion. Definitely fondant the cake first. You only have to work with small sections at a time. Roll out and cut the right height and a length you are comfortable to work with, fold the leading edge under and then work the length into pleats using a satay stick / bamboo skewer - obviously they can be as wide or close as you like, you can also choose to flaten the pleats a bit or leave them full and "puffy". The pleated section then gets glued to the top edge of the cake - and you continue around placing each section over the top of the end of the last - you then tuck the last pleat under the first so there is no visable join. I often then do a "swag" to cover the top edge where the pleats are joined to the cake. Roll out some sections about 1 inch wide and maybe 3 inches long. Lightly tuck under the edges on both long sides and gather them long ways like material - then pinch the short edges and attach to the cake allowing the swap to drap nicely (not pulled tight). Go round the whole cake and then attach a decorative button, flower etc on the joins.
I can't take credit for this - thank Kerry Vincent. It is really much easier than it looks - finished product is just amazing.
Have fun with it![url][/url]