A figure of eight pattern is almost deaf on the side, which can help when recording an acoustic guitar and a singer at once. If you aim the side of the guitar mic at the singer's nose, you'll get very little bleed of the vocals in the guitar mic.

The fig 8 is a must have when you want to record with an MS stereo placement.

You can find all about MS and other stereo placements at the DPA site (dpamicrophones.com), or do a search on the forums.

Figure 8 is also great when you're recording background vocals - you can have multiple vocalists on either side of the mic.

Read up on M-S micing. I found it very useful for recording acoustic rhythm guitar.

Figure 8 is also nice if you want a little more room sound than you'd get with a cardioid, but not as much as you'd get with an omni. You can easily adjust the amount of instrument/voice sound versus room sound by rotating the microphone just a little. Because of its great rejection characteristics, you can actually remove the instrument almost completely to get an extremely "roomy" sound if so desired.

-Duardo