It is a Safari bookmarklet and/or Firefox extension that, when it spots a street address on a web page, will let you right click the address, ask for an email, and then send that address, in convenient Google maps format, directly to your iPhone. It's all of the iPhone's Google maps functionality, without any of the actual address-typing that usually requires.
Lazy? Perhaps. But I can see a sliver of a demand there-- what if you're rushing out the door to the pizza place, but didn't remember to print out the directions and don't have enough time to write the address down to punch in later? Like many things in life, you might not realize how necessary this little extension is until you actually have to use it.
Thanks, Matt L!