I know it has just been implemented, when you complete a quest and it is in your profile and you then hover over it, the information box that pops up should include a number out of total (EX: 4/5) to let you know how many quest you have completed for that game out of the total for that game. This way you can know what games you have to revisit to complete a tricky quest you may not have finished.
Also, if you could sort the quests in your profile by game, (along with date earned),and maybe even by difficulty too.
I know this stuff has just come out and I also have no idea how difficult these ideas would be to implement, but I want to know what people think. Also, this quest are lots of fun!