I've been trying to test using checksums to access pre-filled Profiles, eg:
/civicrm/profile/edit?gid=1&cid=12&cs=12f12df65c25b4b31afb11726af4d5ca_1438265969_168
However it does not seem to be working in the current version of CiviCRM (4.6.x). The profile appears without any information filled, and there are no error messages displayed.
Using the same approach (same contact ID and checksum) to pre-fill an event form is working fine, eg:
/civicrm/event/register?id=442&reset=1&cid=12&cs=12f12df65c25b4b31afb11726af4d5ca_1438265969_168
Is anyone else experiencing the same problem? If so I'll submit a bug report.
Documentation for checksums at the bottom of this page: http://wiki.civicrm.org/confluence/display/CRMDOC/Tokens