Have used this a bit before - including locating the Townsville airport and sending my husband directions via SMS to the beach when he was up there for the airshow last week!
I've also used it to view accomodation locations in unfamiliar cities - Sydney, Adelaide, and some places in New Zealand. As we quite often use public transport in major cities and travel with 2 small children, we always look for accomodation that is easy to access with a pram (helps to see where stairs or really big hills are!) and close to rail/bus routes - google maps has been wonderful to use for this.
I love that you can see map, satellite and terrain formats in one place (how much better than a street directory!) and that you can zoom in & out to see the surrounding area (no flipping between six different UBD pages). I also really like the 'get directions' feature - have used this many times too.
Haven't seen whereis.com.au before though - very similar and easy to use.