I have (gulp) ten, but each has a different niche.
7x35 - one (old wide-angle porro)
7x42 - one
8x30 - three (old porros)
8x32 - one (modern)
8x42 - one (modern)
10x40 - one
10x50 - one
12x50 - one
The 8x42 in particular is my "no excuses" binocular, used in situations where performance is vital. The 8x32 and 10x40 get used when travelling, or in less demanding conditions (shorter distances, good light) - I like to have the choice of 8x and 10x magnification for when I prefer a wider field of view vs. a closer look at the birds. The x50s are used for medium (10x) and long (12x) distance observation.
These are currently my most used binoculars. This year I think I have probably used the 10x40 about 30% of the time, the 8x32 and 10x50 about 20% each, the 8x42 and 12x50 about 15% each. The unmatched field of view of my 7x35 is wonderful, but I find the birds look a little smaller than I would like in 7x magnification. I love my old 8x30s for their lightness, wide fields of view, and the fact that they are such a pleasure to use (I think the nicest of all my binoculars to hold and to handle), but of late the birds I've been after have been flying far - at times disappearing from view even with the 10x50. I've used them a lot in the past, have had many good days with them, and will use them again, but not right now.