If you chose to go with C++ for the client, please go with GTK+. On my Linux Netbook, I am running a lightweight Window Manager (PekWM), and Qt dependencies are avoided because they generally take up too much disk space (which is important, considering I only have an 8GB SSD on my netbook) compared to GTK+, as they like to add in extra garbage KDE stuff a lot. Not to mention, that my widget theme is GTK+, and I don't want to install an extra program to make Qt use it, and I don't even have Qt installed. At all.
I would prefer a GTK+ based C++ app though, or maybe even PyGTK, as it would let me get rid of the horrible looking non-native Java theme in Linux, even though I did make some Java apps of my own in the past use GTK themes properly (very small apps though, such as a dice roller - nowhere near the scale of Shoddy).
I'm probably going taking C++ as one of my classes next semester, either this summer or fall, and I will be learning how to implement it with GTK apps, either in the class or by myself. If the project is still going by the time I have a decent grasp of the language, I'd be more than willing to help, but that may obviously not work out.
Also, it may be a good idea to utilize GitHub or Google Code for public code submissions.