I noticed that when I upgraded to 2.3.3 I was no longer able to login to my blog due to the 'cookie' error. Though easily bypassed by temporarily renaming /plugins to /plugin via FTP, logging in, re-renaming the plugins folder back to /plugins, going into the plugins admin, deactivating all, and then bringing them back one by one to see what messes up... I've found that the only one that errors out is the WordPress.com Stats plugin. Everything else works great, and even if it's the only plugin activated it starts tossing header errors, blank admin pages, and prevents logging into wp-admin due to 'blocked cookies'.
Anyone else getting this issue or have a suggestion for a fix?