I own a Carvin DC727 that I installed DiMarzios into.
The Good: The guitar sounds and plays fucking-amazing. Great tone, great playability. One of the nicest playing instruments I have ever laid hands on. Love it. Carvin was the only way I was getting an ash bodied, ebony fretboard 7 string with decent quality under $2k and in less than a year of waiting time. $1100 and 8 weeks of waiting is a killer deal for a guitar this good.
The Bad: The hardware, electronics, and pickups they ship with are, shall we say, not that great. I had three main problems:
1) The pickup routes. I don't mind cheap/generic pickups in a guitar, since I'll probably be changing them anyway. Would I prefer pickups that actually have resale value? Yeah, but it isn't a deal breaker. What annoys me is that the pickup routes are too small for every pickup that isn't a Carvin. It took me about 40 minutes with a Dremel tool to route the holes to be large enough to fit the DiMarzios, but it doesn't look that great, and really should have came like that from the factory.
The pickups fucking suck by the way. Extremely thin, like a highpass at 200Hz or something.
2) The tuners. Sperzels. Maybe decent for a 6 string that's going to be kept in a higher tuning, but they are a poor choice for a 7 string. Reason being: They won't accept a string larger than the stock .056 gauge, which (when tuned to B) is roughly equivalent to a .042 in E. This is "Extra light gauge". In order to get fatter strings in there, you need to drill out the tuner hole to make it work. Given that Sperzels only have a 12:1 ratio anyway and aren't terribly precise, I'd rather just replace them with some Gotohs. Unfortunately, Gotohs don't exactly fit in the headstock perfectly, so one of them has to be a little crooked. Doesn't bother me a whole lot, but it makes tuning something of a pain.
Tuning stability with the Gotohs is markedly better than with Sperzels. Oh, and I can fit a .068 with no trouble, which is about equivalent to a .052 in E. Glorious tone victory.
3) They don't really want to work with you. I emailed and requested that they route out DiMarzio routing holes and drill out the tuning peg so that it would accommodate larger strings. They refused. Wouldn't even put a price on it, just categorically refused to do it. I understand that they've got a certain way of working, but if you offer 'custom' guitars, you should be willing to fucking customize then when offered cash to do so.
I love the guitar, but it certainly didn't come as a 'finished product'. Took an irritatingly large amount of work to get it to be awesome. That said, it IS awesome, and I would definitely order another one...
Oh -- and I hate that only the 7 strings have a 25.5" scale. I'd totally get a 6er if they didn't use a 25" scale.