1) Why you have that as your desktop? Do I really need to explain this? =) I love the Phoenix, and it's an awesome image. It's become my default wallpaper I come back to when I get bored with something else, until something new comes along.
2) What's so special about it? Pretty! Fire! One of the best Phoenix images out there, and makes an amazing looking wallpaper.
3) Does it mean anything to you? All things are reborn in fire.
4) When will you change it? Eventually. Probably when Marvel puts up something nifty. It's a pain trying to find images that are widescreen that I like, or that are large enough to edit and trim to fit my screen and not get hacked up to the point where the image sucks.
5) What will you change it to? Most likely another comic related image. Maybe WarCraft.
6) What was the previous desktop? Marc Silvestri's Ghost Rider variant cover.