The biggest mistake
Log4J was already established as the best logging framework when JSR-47 came round, but the JCP said "not invented here" and had to come up with their own (crap) version. Result? No one, but no one, uses java.util.logging, while log4j is the first jar file I add to any new project.
Even when Apache asked very nicely for them to modify JSR-47 so that log4j could become the default provider, they said piss off - despite the fact that several other JSRs issued revised versions as a result of feedback from the community (JMS 1.1 did away with P2P and P/S domains, for example).
If the JCP wants to change, and wants to show that they have changed, the first thing they should do is throw away java.util.logging and incorporate log4j into the JDK (or at least provide an SPI so that log4j can be the default provider).