The biggest visible change is the addition of that keyboard – it could well be just a temporary addition as Nokia have said one is coming in the next firmware update (at least for Symbian^3 devices), but in the meantime this is a great substitute and mirrors the approach that Opera have taken. For a piece of code that has a limited lifespan, this is impressive.
The Gravity interface has also had a general spruce up, with more rounding on the corners, the Symbian^3 full screen mode available for S60v5 devices, transparency effects, some shadows, and more small flourishes to improve the UI.
There are also a number of changes in how Twitter and Facebook 'work', and the ability to preview images from Instagr.am in the client.
Available direct from author Jan Ole Suhr, there’s more on the alpha release at Mobileways.de, where you can just grab the SISx installation file direct.