How often do you use fill-in flash?

All the time? Even on the brightest of days?

It's on the brightest of days it's really useful. If the ambient light is dull, then everything is lit about the same, so no fill required.

I nearly always have a flash in use when I am shooting. Unless it's landscapes. Then I need two. :P

The brightest of days is when you need it most.

Check out the link in my signature on how to use flash outdoors.

apersson850 wrote in post #8849303
It's on the brightest of days it's really useful. If the ambient light is dull, then everything is lit about the same, so no fill required.

Agree!

Agree, as much as I can.

(I don't often have it on the camera though using PW flex system.)

Virtually all the time

I will use fill flash virtually all the time when shooting people or pets at distances wherein the flash can be effective. When shooting wildlife, I will always use a flash, even when the distance is too great for the unit to provide effective fill. Even at a long distances, the flash will usually place catch lights in the animal's eyes making them seem more alive.

I carry a 17-55mm f/2.8 IS and a 70-200mm f/4L IS lens on two 1.6x cameras. I have recently purchased a 270EX flash which remains constantly on the camera with the 70-200mm lens. This tiny flash only weighs a couple of ounces but can provide fill for informal, outdoor portraits. Its profile is low and the flash never gets on my way. I just turn it on and off as I need. The recycle time is very quick, especially when I use it at -2EV for fill light.

The 270EX has HSS capability so I don't have to worry about keeping my shutter speed below 1/250 second when shooting outdoors.

I have accessorized the 270EX flash with a Joe Demb FlipIt Junior diffuser/reflector. This accessory really extends the versatility of the 270EX.

I can get rather nice lighting for smaller areas and the light doesn't look bad as the main light when the camera is in the vertical position. This feature is important since the 270EX only tilts but, doesn't rotate. If it were not for the FlipIt Junior, I would have problems bouncing the flash when the camera is in the vertical position.

The 270EX is certainly NOT an all-around flash unit but, is great for my purposes.

i would like to see some samples =)

Here are few examples. I use flash as fill in all photos.
In first 3 photos I use 100mm macro lens and at last photo 500mm lens.

1

As stated above by most, I use it outdoors when the sun is harsh, or when I am shooting under foilage, and so on. Most people around me think I am crazy having my big 580 mouted and firing when there is plenty sunlight outside.

Only on product, never on people, I move to better lighting since I usually blur out the background and not stuck to any one place. I used to also with my G9 on flowers when up really close and I'd have it turned down all the way.

One of the few good uses for the pop up flash. I use it or the 430ex often when outdoors.

I also use the flash quite a lot, bright days especially, but mostly off the camera if I can.

Pretty much all the time. I paid a lot for for my 580EX II. I'm going to use it!