From my perspective noise reduction is the one remaining obvious thing missing in picasa’s simple photo editing tool kit. Unfortunately the best NR (that's Noise Reduction) Software is still relatively expensive and mainly available only as plug in for Photoshop & Lightroom. Don’t despair, a free download trail of noiseware (either as a plug in or standalone) will give you decent results before you need to fork out big bucks. The above example was created with the Noiseware Community Standalone version (free and no trial period). Good Noise filters are available for Gimp.
There is a lot of hype written on the net about NR tools and most are actually much of a muchness, but without testing it is difficult to appreciate subtle differences. Pro Photography Show gives a decent review of leading NR software by way of a number of downloadable high resolution before & after images so you can see for yourself.
It is wise to have at least one such NR filter method available to help you recover an occasional dark photo or even a whole series from your party when the photographer may not have be concentrating.