Who has done a 360 degree performance appraisal system? What are the pros and cons of this system?

For bigger Organization (workforce of over5000) it is complicated and time consuming exercise…it would be better if360 evaluation should be restricted for the higher ups….as higher ups (sr.
management) employees are few in number….
While doing360 it is required to keep confidentiality as senior employees are being evaluated by their junior employees and their negative ratings may have lashed back….
There is a fear that subordinates leak information to each other and settle evaluation between them if they are doing each others….

I have known of companies that use360 degree evaluation system however I believe that it turns out to be more of a popularity or personality related appraisal because not everyone may really knows what all employee's job profile and work is.
I also agree with Aziz on all his inputs.360 degrees appraisals are best in use with extreme confidentiality for senior management roles since they affect the functioning and decisions of the Company.

I have done360 DF -implementation, administration& CI for past7 Years.
The360 DF system works well in a following environment:1) A well establish & well internalized( by employees) competency framework in the organization2) A matured group of peer/subpeer/ Appraiser & Appraisee .
Hence advisable to be administered to > mid management.3) To top it all , the organization should have a clear objective why it has to go for a360 df.
( I had given high weightage for360 DF in case of a candidates considered for promotion or development purpose only, though we had a30 % weightage for this on overall competency rating-just to reinforce the organization competency among the employees)4) A Feedback or feed forward organization culture ( people readiness to accept constructive criticism & people readiness to give objective feedback).
Hence due readiness check has to be done before you go for implementation.Go for a top down approach while implementation ( senior folks -mid -junior in that order in a spread of5 years) and once implemented do a continuous Plan Do Check Act & enablement/training series ( i can share some interesting video on the same /session materials) If managed well the PROS of this system Overshadows the CONS.
Remember: Any new system is like a sapling, it needs a fertile ground( organization) & constant nurturing ( buy ins) + occasional weeding ( incremental changes) to become a self sustained plant/tree ( system success).
With highly evolved systems & well planned timelines, the hassles in administration can be overlooked.