Agreed - I would really love that feature which would allow me to somehow only show what I was looking to collect in a given set vs. what I currently have - then show that percentage. Maybe the following formula...
Cards I Currently have in that set (not including the ones for sale/trade) / (Cards I currently have in that set + the cards I have on my want list) = % shown on set collected.
Like you and the Cubs, for most sets I am only looking to collect the Brewers. So, if there are 10 Brewer cards in the set and I have 4 and there are 6 in my want list = I have collected 40% of the set.
I am thinking it would be a nice feature to see that in a quick glance to see my goals and then maybe a way to print that list as a reference.