Just want to add some comments and share my experience with Eclipse plugin that uses older version of plantuml.jar.
Not been experienced with Eclipse plugins authoring or not able to find actual source code for Eclipse plugin as well as time constraints from my side did not helped ether.
Everything was continued to work on my old Linux Mint 13 installation with eclipse and plugin though not on Windows.
Finally I've decided to downgrade Java version to 6u43
Now it is working again.
My environment: Windows 7 64bit, Eclipse Juno, Java 1.6.0_43-b01, Eclipse PlantUml plugin net.sourceforge.plantuml.eclipse_220.127.116.1150, Graphviz 2.80
BTW, Graphviz 2.30 with Eclipse plugin have layout issues with Activity diagrams.
Ones Eclipse plugin will get updated with the latest PlantUml version, I'll be trying updating Java again.