I can't stand to see a good question go unanswered, Danny.
I can't speak specifically for RDP Demo, but I can tell you about the RDP apps in general.
RDP stands for Remote Desktop Protocol. It's a protocol developed by Microsoft to support their Remote Assistance technology and Remote Desktop features. All Pro versions of Windows come with the software pre-installed.
The protocol is designed to "remote" the user interface as efficiently as possible. To do this, it sends vector graphics (commands that draw stuff, rather than the pixels the stuff is made up of) to the client, where it is rendered much like it would have been on the PC.
So, RDP implementations in general provide a full-featured PC remote control experience, letting you see the PC screen on the remote device, and giving full control over the mouse and keyboard.
RDP is not available in Home versions of windows. It is available as a 3rd party application for some Linux distro's.
VNC is a very similar program, but since it is not built into the operating system, you have to install an app on the PC. VNC differs from RDP in that it sends actual pixel data from the screen, so it's generally not as efficient.
RDP has the potential to provide the fastest user experience because of how it sends graphics. However, it also often suffers from quality issues because it may decrease color depth and remove some graphics in order to improve performance.
RDP and VNC both have one drawback in common: they are "point to point" protocols, so they're best for network-savy users. To make them work, you must configure the phone with the host name or IP address of the PC so that the phone can connect to the PC. This is often not possible in corporate environments because of firewalls, and even at home it can be a nuisance because your ISP is likely to change your IP address from time to time.
Our product, PhoneMyPC, is very similar to GoToMyPC or LogMeIn, in that it is a hosted service and "just works" without any special configuration. It also works perfectly in corporate environments.
PhoneMyPC uses a technology most similar to VNC, in that we send actual graphics data, so there are cases where RDP would provide better performance. However, we chose the technology we did because bandwidth availability is steadily increasing, and we wanted to provide the best visual experience possible. What you see on the phone is exactly what you would see on the PC; no compromises.
PhoneMyPC is also the only remote application (in fact, the only Android application, that we know of) to support multi-touch zooming since Android 1.0.
Cheers!
The PhoneMyPC Team
SoftwareForMe.com