I threw some data into the demo on my Macbook Pro and within an hour had a pretty damn good image, better than I would have gotten in Vray/Mental Ray in that time, so I ponied up and bought a license, build a proper GPU rig and am now loving it and looking forward to seeing Octane evolve. I've also been telling all my friends, some who found it before me and weren't so kind to show me the light sooner

So, I am using the standalone and not the plugin. Why? Well, because I am cheap and I have a license of 2013 and Autodesk is being a pain about getting the update to 2013.5 for me so I can use the plugin for my ancient license. That is all good though, because I like to work with the native rendering interface to really learn the in's an out's before I have to navigate the plugin and the equivalent Maya nodes.
With that said, there are some things in the standalone that make it a little frustrating to use. I could put together a list, but most of them are just things that getting more familiar with it would solve, like picking materials with the material picker instead of selecting them in the outline panel, so that the viewport doesn't shift to the object node instead of the render target...
The only thing I would really like to see is some independent control of the viewport resolution and final resolution. I really want to be able to work with framing up my scene using a scaled preview of my render target, while the render is actually rendering at the full resolution. Currently, I have to set the resolution, and pan around using the sliders to make sure the shot is in frame, or adjust the scale down, frame it up, and then adjust it back up. I understand that some of the plugins actually do this, but I have not found a way to do this in the standalone. Perhaps I just suck at googling how to do this if it does exist, but if it doesn't, please think about adding it to a next release.
Thanks!