From the Changelog:
- Binary formats
- Simpler, more powerful I/O format API
- Native binary format with support for all R data types
- Worked around an R bug that made large reduces very slow.
- Backend specific parameters to modify things like number of reducers at the hadoop level
- Automatic library loading in mappers and reducers
- Better data frame conversions
- Adopted a uniform.naming.convention
- New package options API
If you are using R with Hadoop, this is a project you need to watch.