Hello, I have been carrying out similar works for last 3 years.
Also, I not only make my Android application connect to a Desktop application, but i connected it to a variety of Wireless (IP, WiFi , Bluetooth) devices. Some of them are medical devices and equipments, some were parts of a surveillance system, and some were sensor devices monitoring and feedbacking on different parameters. Some were to control a device from a Phone,.
In my household, I use my application to connect to a device (Fully designed by myself) to turn on/off electrical appliances etc.
I also delivered a product to one of the companies i used to consult for a year back, which could soft reset wireless routers using one's Android phone.
For myself, when i teach my Masters degree students, I use my android mobile phone to control the Power point slide show that takes place on my Laptop /desktop running Windows / Linux /MAC Operating Systems . I shall shortly send you a link of this project hosted on Google Android Market.
Regards