When selecting this device, I was specifically interested in inexpensive devices using FireWire 1394 only, as I'd max-ed out the native USB ports on my iMac, and I did not wish to run through a USB Hub, because I saw nothing but heartache there.
I use this with an Oktava condenser mic and with a few inexpensive vocal mics to record vocals and acoustic instruments with Garage Band and Ableton Live 7
I am using this device with my Intel iMac Dual Core 2.0 GHz, with 1GB of RAM (which I may just upgrade to 2GB)
It has dual 1/4" and XLR, and LR RCA input. While you can use more than one input at a time, my purposes haven't called for it. Also, you can use several different types of output for monitoring, ranging from an 1/8th" headphone jack and a 1/8" line out to or RCA outputs for powered monitors.

I purchased the Inspire GT Limited Edition model, as it was more aesthetically appealing to me. The Inspire GT driver did not work properly with my Mac, but when I installed the Inspire 1394 drivers, everything quickly fell in to line. I find it compatible with all of my equipment. I've experimented with different mic setups for acoustic guitars, and even run the stereo outputs on my POD XT Live in the 1/4" inputs, and it's given me some creative flexibility.
Configuration was a breeze, and after installing the correct driver I was working in a flash.
The manual was a bit sparse, but PreSonus online support was sufficient.

The drivers are stable enough for my needs, and hobbyist/entry level users should find the features in the driver easy to work with. I am getting limited latency with Live and GarageBand, though I'm sure if I add ram, this will get better. At the moment, I'm one track at a time, working as a single musician.

In this price range, there were only a couple interfaces to choose from and presonus has a good reputation and from reviews I read the Firebox produced less latency due to the high speed firewire connection as opposed to USB.
I used this interface with a homebuilt 1.3ghz PC with a gig of ram, and Cubase LE which was free with the Firebox, and my wharfedale 8.1 monitors. I was mostly using it (and its phantom power) to record acoustic and electric guitar with a large diaphram condensor mic, I rarely went direct through it except for bass which it handled nicely. Having 2 quality XLR inputs right on the front is nice so I'm not groping around back. It would have been nice to have all the inputs on the front, but.... I only use 1 or 2 anyway.
I have to say, this thing is pretty beefy with its metal case and metal knobs. As small and portable as it is (a huge plus for those of us on the go with our gear) it would have been nice to get a dedicated carrying case instead of a foam lined package it comes in.

The software installed no problem, compatible from the get go which is great because I am NOT a techhead. Cubease LE was a bit of a challenge getting the settings on the Firebox ready to record, but the manual helped.

Once I got it rolling, I never had a problem with the software. I only got noticeable latency when I was using my Drumkit From Hell which hogs up the ram on my computer, and it was bad. I only recorded one track at a time so I guess I've never really put it through its paces, it can record 4 simultaneously.