I've got the following set-up:
Apple TV 3
When using SlingPlayer for iPad 3.2 or below, I was able to avoid the issue Slingbox Support - Known limitation when using AirPlay with the Slingbox PRO-HD or SOLO by using Airplay mirroring. The image filled the screen, and all was well.
However, since upgrading to 3.3, this is no longer possible. The iPad screen is now truely mirrored (meaning; 4:3, with the status bar on top, SlingPlayer menu controls displayed, etc., instead of filling the screen, without menus etc., as before), and the image is not displayed on the TV or the iPad - only the audio works. In other words, 3.3 has broken Airplay mirroring for me. I've had to downgrade to 3.2 so that I can continue getting a proper Airplay image.
I must also emphasise that this issue does not exist if I use my iPhone with the latest version of SlingPlayer for iPhone (3.8.14). Only the iPad app has this issue.
Please include a fix for this in the next app release.