Heisig teaches you how to write each kanji from memory based on an English keyword that is 'a' meaning of the kanji (that is, each keyword is a definition of a word that includes the kanji. In a few cases, it's a really obscure word, and in a few cases most people would consider the meaning to really belong to another kanji in the word, but in most cases it's a meaning for a common word using the kanji.)
The technique involves breaking the kanji down into constituent parts that repeat, which he calls 'components'. Some but not all components are radicals, some but not all of the non-radical components are kanji in their own right (which is why Heisig includes some obscure kanji - they are subparts of other more complex kanji.)
Obviously, while you've only learned to 'write' the kanji, the ability to write a character from memory makes it easy to recognize. The semi-meaningful keyword makes it easy to remember when you see it used to spell words - the closer the word's meaning is to the keyword, the easier, but even when it's not close you still have a 'name' to hang on the kanji and a detailed knowledge of its structure, making it easier to remember.
It's a little indirect, obviously, but I found it highly effective. Also, being able to write the kanji really is -very- useful -- almost every IME has a handwriting input, so when you don't know how to pronounce a word you can still write the kanji into your IME.