My wife is very tolerant as long as I exercise by riding one of our bikes. I/we currently have 28. All of them are ride-able. But about 8 of them are in need of serious rebuilding. Most of that group will be flipped and at least one Mongoose is a donor bike.
My two sons and I ride about 10 of them and another 3 are Vintage or Classic. Those three are:

83 Trek 560. In fair condition, 100% ready to ride, but has some scratches and deterioration. Nice Reynolds 501 frame, this was the first Trek road bike to use Aero brakes.

91 Nishiki Ariel MTB, elevated chain stay, Cunningham design with period correct Scott "Clark Kent" suspension fork and updated with V brakes. This bike is my first build and is 90% complete.

82 Fuji Monterey, not a particularly rare bike or unique, BUT it is in immaculate original condition so I'm having trouble parting with it.

I currently have three bikes. The only difficulty is deciding witch one to ride. Sometimes, I feel sorry for a bike and take it out for a spin.

I had three. I donated one to the bike and book mobile then I donated my girlfriend's Magna and gave her my Trek. I'm going to pick up my WOW classic (anyone?) tomorrow and the miyata 1200 should get here this weekend.
I have three...

Three is the answer.

My answer is probably too many. As far as the wife goes, she doesn't mind at all as long as I don't insist on her having more than three.

We're about to move and moving alot of bikes is somewhat of a challlenge. The solution? Rent a bigger truck!

The picture shows some of the bikes staged for moving day. The handlebars are turned and the pedals removed. The bikes that don't have kickstands are hanging till loading time.

I think having one bike for every kind of riding you do, plus a few bikes for fun is just fine. Once you end up with bikes that don't get ridden for 6 months, you probably have too many. I think when you have more projects than rideable bikes, you have a problem. I definitely have a problem.

Rideable:
92 Miyata 714: main commuter
94 Trek 850: Snow commuter/MTB
Tall bike!
Giant Butte: uber beater locked outside at work
60 Hercules 3 speed (needs some love)

Projects:
78 Maruishi Roadace 707: building a fixed wheel next week
01 Specialized FSR Enduro Pro: Need a rear shock
Leader something or other: This will be my fast roadie, in case I decide I want to race
89 Cannondale MTB: will probably be a SS cross country
70 Stingray Fastback- need a 5 speed stick shift ($$$!)
7? Peugeot U08- may replace the Trek as a snow bike.
24" Rat rod/low rider project
Jamis Eureka: may never get built now that I have the Specialized and the C'dale, maybe for the wife.

The bigger moving trucks do come in handy!

12 functioning bikes + 2 projects. I won't bore you with the ridable bikes (not yet, anyway!) but the two projects are a NOS Giant RS 920 step-thru frame and fork and a '81 Schwinn Traveler 68cm frame. Both lugged steel (the Traveler I'm going to sell once I get it fixed up since it's too big for me to ride).

Well that is hard to say. I have not been cycling very long but I have caught the bug in a bad way. I have a 1989 Miyata Sportsrunner ATB, 2006 Specialized Roubaix, 2007 Specialized Tricross Comp Triple, 2007 T1 Trek fixie, and an early 80's Windsor International that I picked up in my travels!

Each bike has it's own personality and feel. The geometry varies as well as the materials used. The ride of each is sometimes subtley and sometimes vastly different! In the end I think the number of bikes is a very personal thing but I see it simply as you can never have too much sex, money, or bicycles!

I have a fast road bike, an ATB, and a three speed for cruising with the kids. Plus a couple of other bikes that caught my interest. I like each bike to be different. When you spend so much time doing maintenance that you don't get to ride, or if bikes sit in the back of the shed waiting to be worked on because you have too many other projects, then you have too many bikes.

I'm starting to wonder whether I might need to sell one or two of mine to pay tax bills and accountancy charges. The really sad part is that the good money would be in my lovely track bike.....

Add another frame to my collection and I'm thinking about a touring bike. That will make five total.

Oh oh. I hate to say this but I have 145(that's right). Most are pre 1980(going all the way back to the turn of the century. I try and ride all of the operational ones to work at least once a year. Luckily for me I live in rural Ontario Canada so I have lots of space. Still another barn to fill up!*lol* I mainly collect CCMs. Cool site. Thanks guys.