The Mirra system is an unusual product, both in concept and implementation. The strange part of the concept is that it's a file server without the ability to share (or store) files via any standard file sharing protocols. One would think that a file server should first and foremost be able to act as networked storage, but the Mirra team apparently doesn't agree.
The puzzling part of its implementation is that while the server portion is built on an Open Source (Debian / GNU) platform, its client side technology is as closed as it comes (Microsoft's .NET). The FAQ section of Mirra's website says they are "currently considering support for additional operating systems", but creating a client for non XP / 2000 OSes will probably involve major work - so I wouldn't hold my breath.
A Mirra representitive told me they've had surprisingly good sales to small professional businesses, who seem to recognize Mirra for its easy-to-use and robust automatic backup abilities. These folks know that data backup is essential to their businesses, but usually don't have the time, discipline or technical staff to do it regularly. Mirra is an excellent solution for these folks...at least as far as it goes.
While Mirra is great at automatically gathering files under its protective wing, it still needs to do more in order to be a really be an install-it-and-forget-it backup solution. Mirra's single hard drive keeps its product cost down, but also is a single point of failure. What's needed is the ability to get those backed-up files into some form of removable media or at least automatically backed up to another hard drive.
This is where the invisible member of Mirra's product architecture - Mirra's online data center - could take on a more important role. It's not too far a stretch to imagine Mirra offering an Internet-based backup service - perhaps for a monthly charge. Enhancement of its remote access capabilities to include the ability to send files back to a Mirra box would also be valued - and perhaps paid for - by small businesses seeking both convenience and peace of mind.
Your buy decision right now, though, should be based on Mirra's current capabilities. What it does, it does well. The question is, will this $400 "digital file genie" grant enough of your file serving wishes?