Something that bugs me from time to time in Photoshop is when the paintbrush cursor changes from a brush tip to a crosshair.

I recently found by pressing CAPS LOCK you can toggle between these two modes – the crosshair indicates Precise Mode.

You can also go into Edit Preferences –> Display & Cursors to set the Painting Cursors between Standard, Precise, Normal Brush Tip, and the Full Size Brush Tip.