I have used it for live gigs and studio sessions with a Charvel Soloist, various Kramer, Gibson, and Fender guitars, and several different amp setups: a Fender Twin, a Marshall power amp and 4x12 cab, and a Roland Jazz Chorus. A nice small club rig is the RP-1 running thru the Twin and nothing else. The Twin and Jazz Chorus really bring out the clean sounds, which are actually very nice. I even created a patch for my old Gibson J-50 acoustic, and am able to get a pretty reasonable interpretation of the natural acoustic sound through the RP-1 and the Twin.
The chorus, delay, and reverb effects are all high quality and very flexible. The compressor is also very usable. Some of the effects, like the reverse reverb, are very extreme and are mainly useful for amazing kids standing around after shows, as opposed to actually using them in a song.
The distortion is a mixed bag. I've found that only two of the four distortion modes - Overdrive and Heavy Sustain - are usable, the other two are too harsh and brittle sounding. In conjunction with the excellent graphic EQ, I've been able to get some very nice Eric Johnson-ish lead sounds, very full and warm with a little more bite. I've never been happy with the rhythm sounds. For hard rock, the distortion is too floppy and imprecise, without a lot of focus or punch.
With the distortion gain and compression cranked up, this is a seriously noisy unit. The noise gate is fairly effective, although it's a little difficult to find the balance between allowing too much noise and chopping off the ends of your long notes. The digital effects are very quiet, however.
I agree with the person who suggested running it at low input and high output levels. The line out signal is pretty hot and will give you all the level your power amp needs, but it clips too easily at high input levels. When you're playing a clean funk rhythm, you can really get some nasty square-wave clipping if you don't keep the input level down some. Also, the cabinet emulator effect is supposed to optimize the output for direct-to-board recording, but this truly sounds like crap. As always, much better to mike your amp.
Other than one of the headroom LED's going out, I've never had a single problem with this unit. I've played hundreds of gigs all over the world with it, and have not pampered it, but it's always stood up for me. You can use it with only an amp for a super-simple rig, or you can use it as a midi controller for a rack unit and even run it in the effects loop of a rack-mounted preamp for a more sophisticated setup. Early on, I played it on many gigs with no backup, because I couldn't afford anything else. After a while, it never occurred to me to have a backup because the RP-1 is so bulletproof.
I've been playing for 14 years, in a variety of styles - rock, metal, blues, jazz, folk, worship band at church, etc. This unit is pretty versatile and is not out of its depth in any of these settings. The distortions are a little generic, but I really like the digital effects.
If it were lost or stolen, I wouldn't cry too much, mainly because my budget is a whole lot bigger now than when I bought the unit and I'd go by the TC Electronic G-Force that is on my wish list. But that's not to say it isn't a very lovable little piece of gear. It's very easy to program, super reliable, gives you one-stomp access to ten patches and access to dozens more with three stomps.
It's important to have the right frame of reference here. You can pick up one of these units used for $150. It's not going to sound like something from Lexicon or Eventide or TC Electronic. But for decent, no-hassle sound on a budget, I think it's a great value.