As a Christmas present I got an Aria Sinsonido AS-100C silent guitar
I've been playing it last few nights when the kids were sleeping, and overall I'm really happy with it. The sound is not the same as in a classical guitar, but the measures of the neck, strings, etc. are the same, so it is great for practice. Playing alone with the supplied headphones is trivial (just need to plug them in ...).
Recording it in the computer is also very easy. With a 3.5mm male-to-male audio cable we can connect the Aria to the Microphone input in the sound card (the "Free Music Intrument Tuner" automatically detects the input, so it provides an easy way to tune the guitar).
Once it is connected, the sound is not redirected automatically (Ubuntu Studio 10.04) to the speakers (or headphones), but with Jack it is very easy to do so by connecting the "caputre" clients to the "playback" clients:
With this in place, I can play the guitar and listen to it via the headphones, and also easily record it via, for example, Ardour.
A first test of this setting can be seen at http://vimeo.com/18801768 (the video was recorded separately and mixed with the sound with Kdenlive. For the video I was using my Pentax Optio M40 camera, which in daylight does a decent job, but at night it leaves much to be desired. Next one will be a decent recording in daylight...)