Sounds great on my electric guitar, and obviously on drum toms...not a fan for using it on vox, but there are those that do. It is also commonly used as kick drum mic, but that it is not my first choice there.
I usually mic the guitar on-axis, and position it somewhere about half-way between the cone and the outer edge to start, then move it around to taste. A few years ago, I was always mic'ing off-axis, but my tastes have changed. Try lots of different positions, closer to the cone for more highs, and closer to the edge for more low end...play with the 5-way bass roll-off switch a bit too...I usually keep mine all the way to the "M" side. (It is a MD421 U5, not the MKII)