I'm also using the "good" word strategy with great success. I was not aware of the whitestring filter until now and I'm using the IMP-filter. As HanSatan and anbuva have already said, the IMP-Filter is another possibility to add "good" words. The Nonspamwords-project is is a small example for this strategy:http://www.texttransformer.org/IPMDocumentation/examplesdefault.htm
With the IMP-Filter some more fine tuning is possible for programming freaks. For example there might be a problem with the whitestring filter, if the domain of your email address or homepage is a "good" word, because spammers often insert these addresses into the text. In a TextTransformer project for the IMP filter such addresses could be separated from the pure good words. I don't know, whether this is possible with the whitestring filter too.