Performance Appraisal

Performance Appraisals are a great time to give employees important feedback about their performance on the job to help them develop their skills, yet companies often just seem to miss the mark. What have your experiences with performance feedback sessions been (good or bad)?  Why is it that companies often rely solely on supervisors' evaluation of your performance instead of looking at peers', customers', etc.?  What are the advantages and disadvantages to doing this?  Do we even need performance appraisals?  What would the world be like without them?  Finally, why are performance appraisals done only once per year (typically)?  Is this adequate?  Please reflect on Performance Appraisals in light of what you have learned about it this week.  Feel free to answer some but not all of the questions presented above.