I agree, I've thought about this too. It'ld be nice to do, but getting the data together would be a real dog of a job.
eg. If you took note of what was flowering in your neck of the woods, thats ok for that specific location. On a map you want to show areas, not individual points. That flower could be blooming from just south of you all the way to cape york, but you'ld not know unless you took a drive up there to check. Do you instead say within a 100km radius of this point? We have a few people on the forum in Oz, but no where near enough to really cover the map. In Vic we're not too bad in we have Geoff in the east, Mardak in the west, Pete on the peninsula and a few dotted around the Melb suburbs. Not many in NSW, one in Tas. Qld Has Slicko and others in Brisbane, Westmar in the south west and Lone (come back Lone. Don't give up because of one bad experience! Stick with it) in the far north.
If someone has a good idea of how to define an area based upon only a couple of points, I'ld love to know.