I've made my own emu, homebrew and application 256x256 icons for Xbox use in fact it is still a project on the go. I use UnleashX as a primary dash with other Xboxes and creating icons that display well in the smaller size my preferred skins on that uses as well as XBMC bigger thumbnails is an art.
I like to use original platform icons or image files from emus (apps, homebrew too) as the basis for the icon but sometimes nothing suitable is available and it is designed from the ground up. I do not like uniform designs for all icons so I try to be as different as possible from emu to emu.
I'm quite OCD about fonts and try to identify the exact ones used for any additional text I might want to add. But in many cases the original font is not identifiable, they're often hybrids or custom created. That 'Playstation' font a lot of icon creators use for instance (Zrnic, also found as PS2 in some places) is not even close to the original PS font used by the games and hardware. The original "Xbox" font is, likewise, a pale imitation of the Xbox logo font which probably didn't ever have a full font set anyway.
This is my current Playstation PCSXbox emu icon. NB. the PCSXbox lettering is done using Zrnic as I thought a surrogate font was actually appropriate for an emulator:-

- PCSXbox Logo C.png (28.76 KiB) Viewed 24560 times
Also a Commodore 64 (Vice64X) one I did recently. Colours, main and background, used are authentic ie. those from the original logo and/or the original console's packaging :-

- Vice64X A.png (29.56 KiB) Viewed 24560 times
A MSX one too. Background is from the emu itself (often used in Madmab's emus) and the logo is an authentic font remake of one of the earlier versions of the emus icon title logo:-

- BlueMSXBox Icon 4.png (31.19 KiB) Viewed 24560 times