Also pay a visit to w*w.st.com and make a text search on PFC. Most apps will probably be biased to the Viper range of products but the data is still valid.
You'll get about a dozen hits with explanations and examples.
w*w.powerint.com
w*w.allegromicro.com
are also worth a visit. Just have a poke around and d/l the pdfs you need.
Most manufacturers of SMPS and power semis have a range of notes on PFC on their sites.