As I explained elsewhere on these pages, the problem of practical I/O between a VM and the resources of the outside world, is one of the most critical problems. UI is one part of the story (thus, my work on Eclipse SWT, the template editor, JSR-287, Squeak Cheese, and other UI work). But no less important is access to data.
This is why, in 1998, I joined The Object People -- the team who created TOPLink. TOPLink is the world's first industrial-grade object-relational mapping tool: our large clients used it for accessing relational data from Smalltalk before the advent of Java.
Today, TOPLink is still the best O-R tool. Yes, I did a lot of Hibernate projects, too; but I still think TOPLink is still way ahead. (And it is the JPA reference implementation, too) Maybe it's just hard for me to be objective...
(Note my use of capitalization -- the first three letters stand for "The Object People"; this is our original capitalization, before the BEA/WebGain takeover in April 2000)