Since then, the small desktop system has only received one major upgrade, and that was when Apple switched from the lacking G4 processors to Intel's. There have also been some minor incremental improvements, but looking at the big picture that's been it for the Mini. We have no idea what the sales figures look like for the unit, but we can assure you the initial craze for the product has slowly faded away, in part due to the reasons mentioned above.
That being said, we don't think it's a good idea for Apple to get rid of the Mini just because with smaller, faster, and more efficient components coming out for laptops - many of which are used on the Mac Mini - those translate in a relatively powerful unit that can potentially attract switchers and thus grow the Apple fan base. Many users are also relying on the Mac Mini for HTPC functions instead of tying themselves up to the more limiting Apple TV. In short, the Mac Mini line looks to be alive for now, with more incremental upgrades on the way.