It's quite reasonable despite being a non-polygonal dataset if all you want is the nearest suburb (this was my use case). They have multiple points for the same location so nearest point search works quite well even with weirdly shaped suburbs. I've mucked around with other datasets (there's an OSM branch in my public repo that i'm currently working on to get down to street and street number level) but for the use i mentioned above the geonames works well.