Be advised, if the cranks are on really tight, the self-extractors won't work (how do I know this?). If the extractors start to come out of the cranks, rather than the crank off the BB, STOP IMMEDIATELY!

Get a pin-spanner (something like this: http://www.parktool.com/tools/SPA_2.shtml) and remove the self-extractor, and use a crank puller tool (like this: http://www.parktool.com/tools/CCP_4.shtml). The mechanic that I asked about the problem I had said that he never uses the self-extractors.