As you can see, the yuan was fairly stable vis-a-vis the dollar until about June 30 of last year, after which it started to show some fluctuation with a trend of gaining against the dollar (or, as the graph shows, the dollar losing against the yuan).
http://finance.yahoo.com/echarts?s=USDCNY=X+Interactive#chart1:symbol=usdcny=x;range=1y;indicator=volume;charttype=line;crosshair=on;ohlcvalues=0;logscale=on;source=undefinedSay you bought US $1000 worth of yuan last June at 6.8 yuan per dollar. You would have received (theoretically) about 6800 yuan. Now, take that same 6800 yuan today, and you could (theoretically) buy 1030 US dollars, for a gain of about 3% in a half year. If the trend continues, you could stand to gain on both the exchange rate, and whatever yuan bonds were paying in interest.
But of course, all that is theoretical. For the little guy, currency exchange fees could eat up the profits, as I found out when I looked at some materials for investing in 5% New Zealand bonds with a Japanese bank. The Japanese government would automatically take 20% of the interest as tax, and the bank's TTB (buy) and TTS (sell) rates were set up so that all the remaining interest would go just to pay the fees for converting yen to NZ dollars, and back again.