For years, serious photographers have always recommended, 'write down your exposure, lens, and filter data.' I always smiled, nodded agreeably, and kept shooting. I found that I was often too busy taking pictures to write down the details. Fortunately, I have an industrial-strength memory for f-stops, shutter speeds, film speeds, and other information, but the perfect combination of settings behind some of my favorite conventional photos is lost in the (increasingly distant) past.
Thanks to digital photography, pads and pens can stay in the camera bag. Every digital camera, from the humblest 3x optical zoom point-and-shoot to dSLR powerhouses like the Canon EOS 5D, stores exposure and lens data as part of every digital photo. It's called "metadata," and it's the key to understanding why some of your photos are great - and some need repair in a photo editor before they can even be called 'adequate.'
Windows XP can use the free RAW Image Viewer and Thumbnailer PowerToy to view metadata from any digital camera, and to view RAW images from some dSLR models.
You can discover the shutter speed and f-stop used for your photo, the zoom lens focal length, metering method, white balance, and lots more digital goodness.
Windows Vista has exposure metadata viewing built into its Pictures Explorer, and you can edit new fields such as Lens Maker and Lens Type:
Any way you choose to do it, you need to check out the metadata stored by every digital photo you take. Understanding the combination of factors that lead to great (or awful) photos can help turn you into a better photographer.