How do you carry them around? I own a tamrac backpack which is now unable to cope with my lenses and filters.
I currently have three lenses for my Canon EOS. Most of the time I use a soft-sided bag with two of the lenses in the bag vertically, and one on the camera body. I do have an aluminum briefcase style case that I use when I travel, or think that they may get banged around a bit.
I have eight lenses plus a couple of teleconverters. I don't carry them all around all the time, one is a 120-400mm monster, but I do have a few camera bags that I use depending on the need.
Day to day, I use the Lowepro Slingshot (I can't remember the model, it was the largest one) and it usually has 5 lenses in it, one on the camera and four in various compartments along with a speedlight and a ring flash, cards, etc. It's a little hefty so I also have a small case that I use for actually walking around and it can only hold a couple of lenses (camera around the neck here).
For travel, I have a much larger case that can hold a notebook computer, the Think Tank Airport Antidote, but still fit the luggage carry on limits. It can take a bit more gear, but is even heavier as a result.
I don't actually a bag that can take all of my lenses if I want to put a camera in with it, so I tend to plan based on what I expect to need for the locations I'll be shooting. However, a few of my lenses are not really daily use types, so I don't normally need to carry them.
I use Lowepro Fastpack which has a nice feature of having side access to the camera compartment, meaning you don't have to throw it on the ground to get the camera out. I use it as for my everyday walkaround stuff (camera + one lens, laptop, other personal items) and when the need arises, I can fit in a DSLR body with telephoto lens, two other lenses, two flashes, and still have room for the laptop and empty generic compartment.
It depends on my needs: I've got four different camera bags (two Tamrac slings, two ThinkTank backbacks) and use the one depending on my equipment needs.
But I never carry around all of my equipment. I pack only what I really need for a shoot. Most times a simple small sling bag with one body with one attached lens is enough for me.
Sometimes I add a tripod and pano head.
Sometimes I add a second lens.
If I need a lot of stuff I usually carry another spezial bag for lighting equipment.
I have a basic large Eastpak bag for daily use. I liked it so much that I made it camera/lens-compatible: took a piece of that white packing material found in boxes for pc's etc, and cut out the exact shape of my camera and most used lenses/filters. Because I made it to fit perfectly, I like it better than any camera-specific bag I ever tried. Definitely worth a shot if you're a bit handy and if you know what equipment you'll carry most.