Fosamax...
Most people take Fosamax without problems, however there definitely are side effects that can occur (like bone/muscle/joint pain described above). Debilitating pain is rare (<1% of people) but still exists. Nausea & other gastrointestinal distress (cramps, acid reflux, diarrhea or constipation) can occur in up to 5% of patients. Side effects that need to be monitored by lab work include low calcium and phosphorous... although even if your calcium & phosphorous levels do decline on therapy, that tends to go away after a while. There are other possible side effects as well, including food not tasting as well. Was there something in particular you were concerned about?
Like Jennifer said, just make sure you sit up a good while after taking it, because it can cause esophageal irritation if it sits in your esophagus. So the general rule of thumb is to take the pill right when you first wake up in the morning with a full glass of water (make sure the pills goes down - you don't want that funny "stuck in your throat" feeling). Don't eat for at least 30 minutes.
~L~