When I plug year end reviews into Google, the first result as very little nice to say about their efficacy. Having spent a number of years at large companies myself I never really trusted the process much, largely because of issues like these - noted the be article above:
If you work in a publicly held company, this means that your maximum raise and bonus have been determined before your personal performance has been assessed.
What's worse is that the good managers who want to reward their stellar employees are burdened with the knowleged that it's a zero-sum game so giving one person more means giving someone else less which often leads to everyone getting about the same. Unless, of course, you're at the top. (ht wikipedia)