I know I cant be the first person who thought of this, but it boggles me that it hasn't been implemented yet:
Enthusiasts want to be Notified when particular aircraft come either to a GPS location or a specified airport (nearby?) so they can watch it takeoff or land etc. Personally, I want to watch one of those Quad-Jet A380's take off or land at San Diego International (KSAN). The A320's are Monsters, but the A380's are Super-Monsters. My personal dilemma is that they don't schedule ANY A380's for KSAN, theyre all up at LAX. Surely in a Blue Moon one will be scheduled for KSAN and many of us would like to be notified when it does.
Finally, one of those enormous Russian Antonov An-225 Mriya's or equivalent is going to land in LA or NY someday and we'd all like to know when that will happen.
Therefore this gives rise to such need abroad for this feature. FlightAware already has alerts for airline, tail, or flight number, how hard could it be to add in Aircraft Type?