I've had a ham radio license for a little over 21 years so I've always been interested in radio but the whole SDR thing is new to me. I still really haven't done a whole lot with it but it's fun to play with.
The neatest thing I did was set it up on the balcony of our 23rd floor condo on Panama City Beach (facing the Gulf of Mexico) and used dump1090 [1] to plot aircraft locations (using ADS-B) on a map. I was able to "see" planes a few hundred miles away (thanks to the height and facing out over the water) but was also able to see them at pretty much ground level.
I have access to a bunch of buildings (mostly on top of big hills) across the southern portion of Indiana thanks to my job and have been thinking about building a bunch of "ADS-B receivers" (using Raspberry Pi's or similar) and putting them out in these buildings so that I can cover a wide area. (I really only probably need about three as long as I put them in the right locations, geographically speaking.)
Edit: I do need to find a good external/outside antenna designed for 1090 MHz, if anyone has any firsthand recommendations.
In addition, at one of these locations there's a communications tower used by a pager company to transmit pages so I've thought about building a POCSAG receiver with one of these devices as well.
Unrelated to SDR, but I'm also planning on putting together a bunch of stratum 0 NTP servers (using GPS) and deploying them at these same locations as well. They will primarily be for my own use at work (ISP) but I expect to make publicly available a few stratum 1 servers as well.