I think a better question would be how many card tricks do you regularly preform. I mean I own trilogy so that means I know at least eleven. However I do preform most of them. I have a core 6 pieces that I will use a few from 6 back ups and 3 pieces that only come out if I need to make a great impression. So I guess I have about 15 card effects that I constantly preform. So I probably know well into the hundreds of card tricks but I really only use 15 or so. Sometimes I remember something that I use to do and throw it in to a performance and sometimes that can replace routines that I have in my act.
Know, as in know the method (but can't perform well)?
Or know as in being able to perform (flawlessly)?
Or, know as in I know that trick (where you do "this" action and the "thing" does "this")?
To tell you the truth, I practise 1-5 card tricks because it takes perfection. It would be better this way than knowing a lot of card tricks that you can lack of.
Most people have already pointed out the obvious fault in this - I went ahead and placed my vote under the number of different card tricks I perform, on average, in a week's time, which is 16-20.
However, I know.... a ton. Doesn't matter, though - You can know all the tricks in the world and suck ass at them.
Umm. At any one time I probably regularly perform half a dozen or so. With a fair few more on backburner (Probably haven't practiced for a while, sitting there waiting to be revived on whim).