Warning: I think this voids your warranty. :) We integrated an IR-LOCK sensor with a 3DR SOLO. This project was mostly for fun, so don't read too much into the flight performance shown in the video. We only had one test session, and we didn't tune any parameters.
You might notice that the flight characteristics are similar to those in Randy's precision landing demonstration (link). We ported his code over to the ardupilot-solo repository for this demo. The repositories used for this test are here and here. Unfortunately, the SOLO does not expose the I2C bus that we typically use to connect the IR-LOCK sensor, so we tapped into the power and data lines (SDA/SCL) used by the compass. (btw, it's pretty cool that 3DR sells a SOLO compass leg)
This video also demonstrates a new landing beacon (MarkOne) that we have developed. Initial details on MarkOne are here: http://bit.ly/MarkOne. Significant improvements have been made to the machine vision performance. Namely, we can operate in bright sunlight over water, cars, etc., without worrying about false detections.
Recently, the precision landing code was pushed to the ArduCopter master, with the intent of having official support in AC3.4. The relevant developer conversation is here, and the ArduCopter wiki entry is here. As always, many thanks to the AC developers and community!