Allow me to point out some of the shortcomings of the NeXT Cube, as well as give you an idea of why we're not all using one these days. First, let me just say that I am a happy owner of a NeXTstation and I'd like to get a Cube. With that in mind...
The Cube was a failure. It didn't fit into the workstation market because it was underpowered and it didn't fit into the PC market because it was overpriced. Not having a market is a bad, bad thing. Compared to the machines Sun and Digital were cranking out at this time, the Cube was a dog. It came with little memory, had a slow processor, and only came in grayscale.
The machine originally couldn't even talk to other brands of computers on the same network. That means your lab of NeXT cubes couldn't mount filesystems off the Sun server your company bought last year. What to do? Buy another NeXT, of course! The magneto-optical drive was slow as well. It overheated. It malfunctioned. Disks for it were expensive. But most importantly, it's just not what people wanted. Sure, it may be cool to store everything on a MO disk. But then, no other computers out there came with a MO drive so there was no interoperability. People like to move files from one machine to another, and the Cube didn't really have a way to do this.
There was almost no software. Steve Jobs insisted that programs be written from scratch for NeXTSTEP. No porting applications from your Mac. Very few companies were willing to do this since the user base was so tiny. Even the operating system that shipped with the Cube was broken. It would be years after the introduction of the Cube before NeXTSTEP functioned properly.
So to summarize: very little software, crash-prone operating system, poor interoperability, slow processor, little memory, grayscale only. How much would you pay for such an outstanding machine? Well, back in the day they could very easily run you $15,000 or so. With more memory, a bigger hard drive, and a support contract, you could spend over $20,000. That's pushing twice the price of a Sun machine from the same time period.
For much more information on NeXT, I encourage you to read Steve Jobs and the NeXT Big Thing
. I sure do love my NeXT, but reading that gave me an entirely different perspective on NeXT, the company.