UUP/SPY (US Dollar ETF/S&P 500 ETF) is very close to testing the May 2008 low of 0.167. It is currently at 0.17. Also check out the relationship between UUP/SPY and $USD (US Dollar Index) since May 2008. (UUP/SPY)/$USD started to decouple in the beginning of 2010, just before the Euro Zone crisis hit (UUP volume in 12/09). It's interesting that the US Dollar Index has made two (or for the time being 3) higher highs since May 2008, while $UUP tested the May lows twice (see last chart). $UUP is based on the "Deutsche Bank Long US Dollar Index (USDX®) Futures Index™" (link). I thought these relationships were interesting. I'd say that UUP/SPY support level is important to hold, as well as UUP support in general. The UUP/SPY chart only goes back 3 years.
UUP:SPY click for larger view (StockCharts.com)
UUP:SPY / $USD