[maxwellito]

You can select, then press 'backspace' on your keyboard. That should do the trick :)

[gecko39]

Hmm.. that's not working for me on a mac. I can select a single triangle? option/command + click would be quite convenient vs select each individual cell... since you could drag to erase.

[rzzzt]

XOR-like behavior for the draw tool without any modifiers would work as well.