NOTE: please take this with a grain of salt from a developer/architect and I hope it is useful as constructive criticism.
Scriptability and add-ons are great, but the basic controls for HF are simply lacking (at least using a mouse). There needs to be a mouse sensitivity and vertical inversion controls builtin…and a keybinding GUI for those of us that use the mouse with our left hand and like to remap controls to familiar and optimal setups.
Additionally, I am having problems with being warped to bizarre locations and falling through space or getting stuck in object; walking movement is too slow and the a run key is not obvious in the documentation. Flying is interesting and gets me out of a lot of stops, but there’s no way to do it using your right hand on the keyboard?
The Entity window is frustrating, with it being blank half the time or refreshing to an empty list in the middle of trying to use it. Adding items OFTEN don’t show up, or take 10’s of minutes to show up and then suddenly appear, sometimes only in the entity list and and not visible on the screen.
Object movement is completely non-intuative given the icons that are present. Rotation doesn’t rotate or does nothing when I click on it and move the mouse. Scaling is very difficult. Movement is next to impossible to get it into a desired location, leading me to resort to typing in coordinates and finding that half the time I’m unable to even type into the text entry dialog. I managed to flip a statue can could not figure out how to get it upright, which I thought would be a simple rotate…
Range based volume for the voice chat can be frustrating if you want to talk and explore at the same time. Maybe there needs to be a “Walkie Talkie” in the marketplace to allow for long distance communication? Also sound devices need to be set/reset on every startup to get audio to come out of any device on OSX.
The technology is great and very interesting and is giving us some great ideas after evaluating with the potential of the system, but my opinion is that it is not ready for prime time yet, which is obvious given it’s pre-Beta status. Unfortunately, it almost doesn’t feel like it’s even Alpha yet. I think a number of things I’ve mentioned above can be fixed through scripting, which I am getting to (someone provided a script as an example for inverting my mouse movement for example) but there are so many things that need polish that it’s not ready for us to use beyond evaluation.
We will be keeping an eye on it, but I thought I would give some suggestion that I could see that will really benefit the software as whole for new and old users, not just those that are refugees from SL.
PS. the responsiveness in the Marketplace is great!
PPS: having a ‘lock’ next to a user that’s in a space that you can’t access would be nice to save time when trying to warp to people in the environment through your contact list.
PPS: Piper and others have been very helpful.
PPPS: I won’t mention the crashes but I choose to send developer reports to Apple every time they happen.
 This product is the first thing I’ve seen that allows for the use of ‘body language’ in non-video internet communication and it’s both creepy and fascinating at the same time. Plus the lip synching effect is great!