I actually have a section of one of my small filing cabinets (the tickler file cabinet) that is exclusively for someday maybe items. Everytime I see something that is a someday/maybe, I put it into a folder that is labeled with the general category of that someday/maybe item. I usually get business ideas, so I have a folder called, "business ideas" in my someday/maybe section.
I also sometimes think, "I should learn french" or "I should learn how to become a better raquetball player"...those things go into my "skill building" folder. and I have a couple of other folders too: Things to Sell, Things To Do.
I don't think I will ever have more than 10 someday maybe categories (only have four now). This way my reference stuff and someday/maybe stuff doesn't get mixed up. I might go through my someday/maybe folders bi-weekly, but I wouldn't have gone through my entire reference system bi-weekly.
I am still implementing all this though so I may change it and/or fine tune it in someway. I don't have a "list" of someday maybe items yet but I will create a file in my pocket pc with the list in it that way I can add or refer to it at anytime I wish.