I too, have used one of these little beauties at work, and despite a couple of cheap touches (peeling covers on the back of the cab already), the sound is immensely good for such a tiny little amp!
Firstly, I noticed one or two areas of confusion earlier in the thread...
The amp is delivering 150W RMS into the single 8 Ohm 2x10 speaker cabinet, if you connect up a second 8 Ohm 2x10 cab into the external speaker socket, it brings the impedance that the amp sees down to 4 Ohms not 16 Ohms, as an earlier poster wrote. This brings the power up to 200W RMS.
Incidentally, we tried this head into first a Mesa Powerhouse 4x12, then an Ampeg SVT610HLF, with the 4x12 giving by far the best sound (we had the drums department upstairs shouting at us about the volume!)
In a studio environment, this little amp would find a happy home. With the DI output on the back, and an effects loop as well, you can't go wrong. The cost of one of these in the UK should be around the £310-330, and if you can put up with the feel of a tiny little amp rather than a back-breaking SVT CL, particularly at lower volumes, this could do the trick in the right conditions.
With the build quality and reliability in general for all the Ampeg line dropping fast, I'd have to say that this is probably the best "Ampeg" I've seen and heard in the last few years. If you've got a USA built Ampeg, hang on to it! I wish I still had my old one...