Trust me, worth it.
I first used arnold past October in the office I work now with a lot
of risk, because it was un urgent 3D I had to deliver.
I didn't have the chance to test it at my home, because my computer
didn't support it.
So I took a big breath and tried it.
Guess what, even if I was an arnold noob that time, the
results were awesome and a lot quicker than the "living dead" (lol) mr.
If you know well Mental Ray you can easily make the transition.
Personally Autodesk with Arnold has eliminated the gap from vray.
Arnold is one word: magic.
*Mental ray materials are fully compatible with Arnold.
We are waiting the new version of Forest Pack that support 100% Arnold
without the need of converting materials ecc