One of the nice features of TIFF and PNG image formats is the alpha channel.  The alpha channel is often used to maintain a "clear" background with these types of images, which is useful for a wide variety of purposes.

However, when I use the much-more-light-weight PNG format to insert to a sketch, the image comes in solid black.  Perhaps I'm missing something here?  JPEG works fine, and I can use the little eyedropper to select a general range of pixels, but because of the compressed nature of the JPEG format, a single color cannot really be selected for transparency.  The selection capacity is much improved in v2010, but the ability to simply use the PNG format would eliminate the need for careful selection and tuning out of the unnecessary image noise.

Is it possible to use a PNG image format for this purpose?  (Is it possible to use a PNG image format at all?)

The next application for such images I'd ask about is decals in PhotoWorks.