Yikes, that starts to sound pretty godawful when you get super close, but I wasn't too crazy about it at 3" either; once again, middle ground ftw!
@Kev. Starting at about 3 inch away from the speaker, progressively pushing the mic nearer (maybe 0.5 inch) then pulling away again:
http://dl.dropbox.com/u/2973685/far near far.wav
Putting a piece of the grill cloth between the mic and the speaker:
http://dl.dropbox.com/u/2973685/without-with-without-with.wav
(first without, then with the grill)
Though I think the grill may actually be killing the sort of highs you don't want in a guitar sound.