nickgammon:
Interesting, I had found I could run at around 24 MHz (note the M) with a crystal but not faster. Now I am motivated to try faster clock inputs, excluding crystals.
Just remember to set your LFUSE from 0xFF to 0xF7 (full swing). And, contrary to what the "experts" here say, running at full swing doesn't draw any more current (at least nothing I can measure).