To use Pwoint.me simply send a tweet to @pwointer in form of "some text at an address" like this:
and it will send you back a tweet* that looks like this:
The key is to include ' at ' in your tweet so @pwointer knows you've included an address.
When people that follow you click on the link in your tweet they'll not only see a map with a marker on it at the location you specified but they'll also be able to get directions to/from that location.
* Pwointer checks Twitter every 2 minutes for new requests