Digital Darkroom: Lightroom Healing Brush Clean Up by Patti Schulze (TMELIVE.com)

[nikkormac]

you can also toggle into and out of healing brush mode by pressing Q. and when you're cloning/healing spots in a good-sized area of consistent color, like a fairly consistent blue sky, it's not usually necessary to drag the brush to choose a source; at least in LR 3, you can simply click and the brush will usually be smart enough to blend the corrected spot nicely with the area around it. if you click and it turns out the brush wasn't as smart as you'd like, just hit Command/Control-Z to undo.

[nikkormac]

to zoom in and out to and from 100%, just tap the space bar.

[CheezInspector]

To zoom in or out, you can also use "control" and "z" key (at least on Mac).