I suspected this was coming, and now it's been announced: IBM is getting involved with the Apache Harmony project.
According to IBM steps into open-source Java project (CNet), "IBM has begun participating in open-source Java project Harmony and intends to contribute code to the initiative, according to a Big Blue executive." So far IBM's involvement is one employee who's contributing design ideas, not producing source code.
IBM's eventual involvement seemed obvious to me. First, one of the main people behind the Harmony proposal is Gier Magnusson of Gluecode, which IBM just bought. Second, IBM has been urging Sun to open source Java; since Sun won't, perhaps Harmony will be the next best thing.
Harmony now has its own incubator project site on Apache. The project is seeking commercial donations of code as well as involvement by individual developers.
Update: Here's an article that interviews Geir Magnusson: IBM backs open source Java (VNUNet).