Usually I convert the .ERF files to Adobe DMG, because DMG makes a slightly smaller file. (I have about 10,000 photos on my computer, so small savings add up!)
I manage the .DMG files with Adobe Lightroom, which lets me crop them and do simple adjustments to the DMG file itself. Then I can export a JPEG, TIFF or PSD file from Lightroom when necessary.
Sometimes, when I want to make a particular effect, I save the original ERF file and process it through Epson Photo Raw. Most often I do this when I want to make black-and-white images, because Epson Photo Raw does an especially nice conversion to black-and-white.