Guitar synthesis has been around for decades, but never became very popular, mostly due to poor tracking. Many companies and models have come and gone, but the only one that I know of which remains is the Roland GR-20. Here's the link:

http://www.rolandus.com/products/productdetails.aspx?ObjectId=592&ParentId=53

When you purchase the unit, it comes with the GK-3 pickup which you install on your guitar. There are also some companies who sell guitar synth controllers. Godin is very popular and has many different models. Here's their link:

http://www.godinguitars.com/godingman.htm

Depending how you work the guitar synth into your music and your performance, it can be a good tool for a variety of styles.

Its a shame guitarists havn't been able to get the full midi control keyboard players have enjoyed for years. Like SOS said, tracking was always an issue.

The controllers have gotten a little better and a lot cheaper though. I have the GR-20 and its quite a bargain with improved performance over past models. For 600 bucks you get a controller and a floorboard synth.

I need to check out the graphtech : http://
and the RMC: http://www.rmcpickup.com/products.html
I believe both of those systems get used in the Godin and the Brian Moore guitars that have synth controllers. Brian Moore: http://www.iguitar.com/

I also recieved one of these as a b'day present from a good friend. Anyone remember the GR-707?!! Its a great playing guitar, but I need to upgrade the synth controller. Dig the stabilizer bar! It really works to control subtractive resonances that threw off the tracking of early divided pickups.: (picture is off the web)

Hehehe yeah I remember those. It's been a long time, but if I remember right, they could only do one synth note at a time, and I THINK they only tracked on the E and B string. Am I right?

The guitar is very kewl looking, even now. Fitted with modern synth electronics, it would make for a bichin piece.

Did you get the synth unit with it, too? If so, does it still work?

I've taken her out on a few gigs, and she has a nice presence, very articulate used as a normal electric. Great neck, trem and pickups.
I don't have the synth or the programmer. The special cable is the deal breaker, its real expensive. Eventually, I'll upgrade the controller electronics, but even without it, its still a great guitar. The neck plays like a lawsuit strat (high end Japanese).

I had the 707. It was fun at the time but like everything else it passed. Honestly, I really wish that I still had it.