I don't have much experience using a plasma torch, but from the experience I do have-
It does cut quickly and easily, and with a very thin clean kerf as compared to an Oxy-Acetylene rig. However, I found that it kind of sucks for fabbing using steel tube. The accuracy and straighness of the cuts comes nowhere near what I can accomplish with an angle grinder with a thin kerf cutting wheel. Cutting through one side of the tube (square) had a tendency to negatively affect an adjacent side, and sometimes even the opposing side. This is not at all desirable when trying to make a perfect cut for fabrication, and doubly so when trying to cut a mitred angle. I also found that when cutting things apart, let's say separating a section of tube from a flange, the arc would curve away from the flange throwing the cut's accuracy way off- it meant having to whip out the ol' grinder again to recut the tube squarely after the fact.
Some of this may have been my own inexperience, much of it was the simple fact that an arc is much harder to control than a nice, straight cutting wheel. IMHO, the plasma torch is brilliant for demolition, not so good for the home fabricator especially when considering the price.
Up until I had test driven my buddy's unit, I wanted one pretty badly and was considering saving up my nickels for one. Now- no. Not worth it to me.