I have had a Retro Duo system (Famiclone) for a few months now and I am very pleased!
Although the NES side's music is not perfect on 30% of games it's still is pretty good.
now I have original NES front and top loaders and of course the SNES and it's mini version but it is so simple to just have one system.
It is a must to have original SNES controlers, and they feel perfect for the NES games.
The SNES side works perfectly and is even plays PAL-EURO and Super Famicom Games! Wich means BS Zelda and Super Game Boy 2 finaly work without any modding!
The only games that don't work on mine are Duck Hunt and Paperboy, and even though the music is a littile off its still great fun.
I got mine for 30$ wiith a 8-bit game from amazon, and when I opened up the box I was amazed at how little it was, the game pins were really tight at first but losened up in a week or so.
I think if you can get past the cons of the NES side most nintendo fans would really like the Retro Duo.
Has anybody had any problems with them?

I've seen plenty of games have graphical glitches with it. Still, I think it makes a pretty decent back up

It's not very good. You should check out the review of it at super-nes.com.

http://www.super-nes.com/retroduo.htm

I have an fc3 system. It plays nes snes and genesis games. I love it and I dont have any glitches with it. Works just like the real thing, without being 25 years old. Im not saying the old systems are bad, just that the copper goes bad on them and you have to replace the pin connectors

I'm not saying it's the best system I'm saying it's a great clone, I haven't experienced any unplayable glitches besides the ones I've mentioned and I do still see how the nes is way better but the snes side is flawless!
I have the FC3 also and it will not play my star fox or super mario rpg games, that's why I like the retro duo the best out of the famiclones!
Thanks for the replies guys!
Martin