As Gizmodo says, Apple uses the technology they buy (Coverflow, for example). We were unfamiliar with the service, but GigaOm describes some sweet features like PushPin, which provided developers with an API that could layer commercial information, crime data, etc. on a map. For a nice example of PushPin at work, check out PolicyMap.
Now for the baseless assumptions. Google maps appear in a number of Apple products, like the iPhone, iPhoto and iWeb. Perhaps Apple plans to stuff their own solutions into those slots. Or perhaps they're after a certain technology from Placebase and not the whole enchilada.
Note that the purchase went down back in July. Seth has also discovered that PlaceBase's founder and former CEO, Jaron Waldman, is now a part of Apple's "Geo Team," which sounds like the Justice League but with Al Gore in charge.