Is it possible per object?
Probably not, but then again I’m not that shader savvy.
Best bet would be to use a higher res block texture(as in, scale up a pixel art with no interpolation).
Hmm, I’m not getting email notification updates any more, weird.
Thanks for the reply. For this instance it’s not really possible to scale up the image. I’m already using 4096x4096.
I want to disable mip-mapping on the skybox. I can’t see why anyone would want a mip-mapped skybox, you get neither closer nor further away from it, and the angle of view is always the same?
I don’t see how mipmaping is a problem on a skybox ?
If you see the sky a little blury it is because your texture is too high rez.
Look at it like this, even if you played it on HD resolution you will not have more than 1080 pixels in height shown on the screen. so there is no need for 4096.
It’s dependent on the lens of the camera how much of the skybox texture is visible. With my 35.00 camera, about 1/20th of the full skybox texture is visible at one time.
Hm. Well, you can disable mip-mapping through the User Preferences menu, but I don’t think that you can change that on a per-material basis…
Yeah I’m aware of the user preference and the command line for turning it off completely.
This is one of those niggly things I’ve wrestled with for a while now.
Here’s some screens of the game I’m working on in the BGE: http://www.flickr.com/photos/59732544@N07/
Can probably see why the skybox quality is important 
Whoa. That. Was. Awesome. There’s gotta be a solution for this. My thread mentioned above doesn’t really talk about handling mip-mapping on textures only… You could increase the mipmap quality on your graphics card, or perhaps draw the texture via a GLSL shader - that may allow you to select GLSL texture interpolation methods.
I couldn’t get this to work in the end, but I realised I could break the skybox faces into separate textures by putting in several pixels of overlap (so no nasty seams).
Also, because the texture is painterly, I can create a tiled brush effect and have it overlay, creating a detail map.
Thanks for the tips though everyone 