There are a few decent applications already installed on the phone, and the option to add a whole load more thanks to the Symbian system (although Samsung doesn't have its own App Store as yet), so we'll rattle through a few of the highlights, all of which play very well with the Samsung i8910 HD.
The game Asphalt 4 is pre-installed, and uses the accelerometer and touchscreen for motion controlled gaming, which is very slick and easy to pick up and play.
Smart search works in a similar way to Spotlight on the iPhone, in that it will let you search both on the device and the internet, depending on what you're looking for, which is a pretty neat service.
There's a dictionary with an extensive word list, a compass which actually works, Quick Office and PDF reader to let you do all manner of work-related things, as well as RoadSync which lets you hook up to Microsoft Exchange for calendar, email and contacts too.
The GPS data section, which was supposed to let us view things like out position, coordinates and map any trip length, was something of a let-down, as it spent most of the time connecting and trying to find out where we were. However, with a bit more perseverance / luck, we think this could be a really handy feature, especially when coupled with the compass (which will make Google Maps' StreetView a joy to use in the future.)
In short, the i8910 HD is stocked full of applications for many different things you might need. The only three things we would have liked to have seen would be a native Google Mail client, a YouTube video viewer and an FM transmitter, especially with the emphasis on media on this handset.