Absolutely I have. It does fine in either small venues or really large venues with good monitors. The spot it doesn't work well is the middle ground where you need the amp to be heard from the crowd or over a loud drummer.
Even with loud drummers (shield or no shield) in large venues, I've been able to mic the champ and point it at myself and hear it fine. That is, if I can be far enough away from the drummer.
It's a great sounding amp clean or cranked and I love being able to bring just the necessary amount of power to a gig. It's more satisfying to me personally than bringing 40w and only turning the volume to 2
I gigged with my 10 piece horn R&B/Blues Rock band with a Carr Mercury (1XKT66 power tube, 1X12) at 8 watts. We mic the whole band but even on a stage 20 feet deep w/me about half way to front of stage I had no problem hearing the amp behind me on a 45degree stand. I had a stage monitor where I was in with the vocals, keys, other guitarist & horns so I had no problems at all - I was able to run the Mercury at just about half volume to keep clean headroom and I use good pedals for the mild OD that I need from time to time.
Yep, 4-10 watt amps are surprisingly loud when cranked up. Add multiple, efficient speakers, and you can overpower a loud drummer. Put a mic in front and with decent monitor support (in-ears preferably), and you can play the largest outdoor festival with a Champ.
Once, a 1970 Champ. 4 piece rootsy type music with: acoustic, electric, bass, and drums. Drummer was really dynamic, I (champ) wasn't even miced. Show was great.
I never bonded with that amp though. Updated filter caps, NOS tubes, Tone Tubby 8" speaker, basically the whole 9 and it was still flubby above 7, even with the bass at 2. I have a VHT Special 6 that is everything I wanted my Champ to be.
I gigged with my champion 600 once with a band. But only because we were playing one of the better places in town with some of the best PA, monitor equipment and I knew the soundguy and trusted him. It still was pretty nerve-wracking, cause you are giving up all control to the soundguy. If he/she turns you down or doesn't pump enough through the monitors, you're screwed. Not much you can do to remedy anything. At solo/acoustic gigs it has worked great for me in the past. Now I'm thinking of giving it away though; once I got into higher wattage and bigger speakers, I don't even practice with it much anymore. Just doesn't have the balls or the detail...