If you have the slightest familiarity with computer programming, and if you're using a Windows operating system with MS Office, you can use MS Access to design the most wang-dang record keeping system imaginable. In one fairly small file, I have detailed records of purchases (equipment, materials, ingredients, etc.), from which, inventory and costs are easily managed, as well as an extremely flexible recipe calculator. In addition to doing all the math for me, the recipe calculator has a place for recording all the details about each batch, including an expandable memo field, so I can go back anytime and add notes, reviews from testers, etc. The whole thing is also searchable, and will collate your info any way you want. If I ever decide to sell, I can easily add customer and sales info, shipping rates -- whatever would make life easier. For now, I'm just using it to fine tune recipes, which I then print out and take to my soaping area. I write notes on the printout and enter them into the program when I'm all done soaping.
It was a little effort to set it up, but now record keeping is another fun part of soaping. I especially like playing with the recipe calculator. It's easy to add onto or change the system as needed, which I really like. But then, I'm a little nerdy that way. I realize most soapmakers, (or most *people*, for that matter) would probably rather not build their own software. If you're up to it, though, DIY is the way to go.