Yeah... it's supposed to get down to 42°F (or 40°F, depending on who you believe) where I live tonight. My plants are pretty mature, so I'm not really that concerned at this point. Sure, it's not good, but there's still several degrees to go before it hits frost/freezing temperatures.
I have to agree with BigCedar though... ALWAYS keep checking, and checking, and checking the weather--as much as possible! I recall the last few years several fall nights when the low was supposed to be above freezing. The actual low ended up being several degrees lower than forecasted, many times around freezing and bad enough to cause frost damage to several plants. I would watch night temperatures like a hawk, or if you're not able to, set up the frost cloth before night falls if temperatures are supposed to reach 5-8 degrees above freezing. Be sure to water thoroughly with plenty of really warm (but not hot!) water if it's already really cold outside and expected to get near freezing.