If you have an enormous fonts collection, you can search for a font using a bitmap sample of one of the glyphs. There are two ways to do it: you can either feed Fontmatrix with a ready bitmap file or use Grab mode that will fetch a bitmap image right from your display.
When you have the image in the raster sample preview, click on the glyph for Fontmatrix to compute its bounding box. If Fontmatrix got it wrong, enable the Tweak rect checkbox and drag corners of a frame around presumed bounding box until it's right.
Now type in the character that is on the sample and press Search button.
You can also watch a screencast demonstrating this functionality.