In some organizations with too high of a hierarchy, even those simple acknowledgements can go unknown.
@ pcharles: I couldn't agree more. Unfortunately this is the case in many organizations where HR system is either ineffective or purposefully flawed. Line or department head sitting over you, doesn't let your accomplishments or performance recognized, just to keep his position secure. In those environment it isn't wise to spend your time and efforts in over performing but rather finding a better alternative for yourself.
it's far more constructive to hear something in the moment than six or 12 months after it happened.
@ Susan: Completely agree. I think Intra company social network can do this job well, but it will only fulfil the purpose if it builds up into annual performance score and used as replacement of annual appraisal.