Until Paolo gets a breather, I'll chime in with some insight.  The main thrust & "selling point" of Reality is that it does the heavy lifting of intrepreting the Poser shader tree & nodes into a usuable Lux equivalent (no small feat) automatically. For example figure skins are automatically converted into the Reality "Skin" material complete with a decently tuned SSS volume for all of the skin surfaces. It even has a "hair mask" option auto generated from the diffuse color to block SSS from eyebrows, head or body hair etc...  The big difference between Reality 3 & Reality 2 for DS is that much of the guts of Luxrender have been opened up for the user to get their hands dirty & create their own Lux textures, in a more artist friendly way, especially if you are already versed & comfortable in the Poser Mat room concept.  He's managed to give the same flexibility in a "node-less" setup. I think you'll find it to be a nice mix between "click & forget it", & a tweaker's paradise :-)

BTW, the RUG (Reality User's Guide) that is very well put together & included with Reality3 will be online shortly to download from Paolo's site, so anyone interested can get a deeper look see before they plunk down their duckets ;-) I'm sure he is swamped on opening day LOL.

You can view the documentation for the earlier DS versions of Reality 1 & 2 right now to get a feel for what's in store. A lot of the concepts are the same, even though the UI & program have expanded greatly between then & now.

On a  couple of features that Laurie brought up, IES files can be added to lights in Reality 3.  You can also add textures to for example use a light as a projector.  You also have indepdant control of the Sun & Sky lights and can use the older sky model or the newer one recently introduced into Luxrender.  GPU Acceleration & SLG support are also included, but given that SLG is evolving at warp speed into a monster (check out the Frankenlux/SLG4/ LuxVR threads on the Lux forums to see what I mean), The GPU features will also see some significant changes & enhancements in the coming weeks & months to keep pace with Lux 1.3 when it reaches us soon. Pose2Lux give you a good way to get into using Luxrender & it's unbiased world, but for a very artist friendly yet flexible & powerful, intuitive, well supported bridge between the two programs, you really can't go wrong with R3.