I've seen those, but they always look cheap to me. I mean actual home-stereo, analog turntables (some of which are quite pricey and intended for DJing). As a musician, one of my future purchase plans is a decent USB analog-digital converter, so I agree with you that the best option is to plug a regular turntable into that.
I have a firewire/1394 A/D that does video and audio. It is compatible with my video editing and rendering software. Have used it a lot. Less now since everything is already digital. But it does come in handy from time to time.
Some pretty cool things that you can do once the audio is digitized. I removed a bunch of pops from my LP rips.
Also, the video software has a bunch of audio filtering utilities. And there is companion software that does a lot more such as removing harmonics from 120Hz pickup. My wedding tape had this problem. What is cool is that once the audio is cleaned up, you can run it back through the software to look for any anomalies and distortion.