Anyone who has taken digital photographs has used (or tried to use) some kind of software to do something with it.  The more you fool around with digital photography, the more you fool around with the software that can help you.  Here's my current opinion, based on my limited experience.

I use ACDSee Pro 2.5 to catalog my photos only.  While ACDSee Pro 2.5 contains a good editor, for editing, I use Adobe Lightroom followed by Adobe Photoshop CS4 for fine tuning because I think they're superior in every way.

Lightroom is an amazing program that almost eliminates the need for any other photo editing software.  Its ability to individually saturate colors and areas, change white balance settings and its ease of custom processing is literally life changing, for those of us who have struggled to learn those functions elsewhere. 

I still use Photoshop CS4 with some terrific plugins made by Nik (Dfine, Color Efex Pro, Silver Efex Pro and Sharpener Pro) so I can (1) remove noise and enhance basic features, (2) convert to and enhance tonal qualities in Black & White, and many other effects, and (3) sharpen specific areas of photos for a variety of outputs.  The custom color, black & white, and processing functions unique to them are invaluable. I use another called Blow Up by Alien Skin to produce the large file sizes necessary for big prints.

A good example is the following photo of four cheetahs that I took on the Maasai Mara in Kenya in August, 2007.  I shot this at f/10 using 1/160 second; we were about 40 feet away and I wanted the cheetahs in focus but the rest of the landscape slightly out of focus.  When you click on the thumbnail below, you will see a two-photo slide show that displays the file as it was taken with almost no processing, and then with the sky only slightly saturated to bring out its true color from that day.  I also used Nik Sharpener Pro to sharpen the cheetahs only--and I mean only those specific areas where cheetah fur appears in the photo. Having this kind of control is very satisfying.

This is the RAW file with almost no processing. This is the RAW file with almost no processing.

This is the same file after Lightroom processing to bring the sky and surrounding landscape to true color, and subsequent Photoshop CS4 and Nik Sharpening tools applied to the cheetahs.This is the same file after Lightroom processing to bring the sky and surrounding landscape to true color, and subsequent Photoshop CS4 and Nik Sharpening tools applied to the cheetahs.

I used Alien Skin Blow Up to create a 20" x 30" print image (the resulting file is gigantic) that, if I dare say so myself, looks mighty good hanging in my office.

For those friends who are just getting started with processing of digital photos, I recommend buying Adobe Photoshop Elements.  It's very good editing software and will do just about everything most people want--and the Nik plug ins work in version 7.