I have been converting a multi-project Ant build to a multi-project Sbt build.
First off, the size of the build file is reduced. Classpath management is very transparent compared with Ant.
Task execution is so much easier in Sbt. Compile is part of the Sbt DSL.In Ant the tedium of the markup and the amount of boilerplate required make Sbt the clear winner
Migrating Junit tests wasn't as easy as one would expect. Not due to Sbt, but due to FixedOrder annotations having no effect. My solution was brute force, run each test separately. The command for the BuildBot worker to execute becomes simply, sbt < sbt.cmds. Don't fight it, run your sbt from a file of commands.
Overall, I am pleased with Sbt.