Is it possible to do a drush sql-sync of only certain tables? I have 4 environments between my local, dev, staging, and production. 

A large amount of content is published to the staging environment on a daily basis, so that is the center of my workflow. Once content is QA'ed in staging it is then sql-sync'ed to production. This works fine at the moment. However, we're now going to allow for user registration/user generated content. Is there a way to push these content updates with sql-sync and never overwrite certain tables? Even more specifically, is there something I can place in drushrc.php that will always skip a list of tables across all environments?
YES
If you know which tables you want to transfer

--tables-list
A comma-separated list of tables to transfer. Optional.

If you know which tables you want to skip

--skip-tables-list
A comma-separated list of tables to exclude completely. Optional.


And here is how I know this:


$ drush help sql-sync
Copy and import source database to target database. Transfers via rsync.

Examples:
 drush sql-sync @prod @dev                 Copy the DB defined in sites/prod to the DB in sites/dev.


Arguments:
 from                                      Name of subdirectory within /sites or a site-alias.
 to                                        Name of subdirectory within /sites or a site-alias.


Options:
 --cache                                   Skip dump if result file exists and is less than "cache" hours old. Optional; default is 24 hours.
 --create-db                               Create a new database before importing the database dump on the target machine.
 --db-su=                            Account to use when creating a new database. Optional.
 --db-su-pw=                         Password for the "db-su" account. Optional.
 --dump-dir                                Directory to store sql dump files in when --source-dump or --target-dump are not used.  Takes precedence over --temp.
 --no-cache                                Do not cache the sql-dump file.
 --no-dump                                 Do not dump the sql database; always use an existing dump file.
 --no-ordered-dump                         Do not pass --ordered-dump to sql-dump.  sql-sync orders the dumpfile by default in order to increase the efficiency of rsync.
 --sanitize                                Obscure email addresses and reset passwords in the user table post-sync. Optional.
   --sanitize-password                     The password to assign to all accounts in the sanitization operation, or "no" to keep passwords unchanged.  Default is "password".
   --sanitize-email                        The pattern for test email addresses in the sanitization operation, or "no" to keep email addresses unchanged.  May contain replacement patterns %uid,
                                           %mail or %name.  Default is "user+%uid@localhost".
   --confirm-sanitizations                 Prompt yes/no after importing the database, but before running the sanitizations
 --skip-tables-key                         A key in the $skip_tables array. @see example.drushrc.php. Optional.
 --skip-tables-list                        A comma-separated list of tables to exclude completely. Optional.
 --source-database                         A key in the $db_url (D6) or $databases (D7+) array which provides the data.
 --source-db-url                           Database specification for source system to dump from.
 --source-dump                             Path to dump file. Optional; default is to create a temporary file.
 --source-remote-host                      Remote machine to run sql-dump file on. Optional; default is local machine.
 --source-remote-port                      Override sql database port number in source-db-url. Optional.
 --structure-tables-key                    A key in the $structure_tables array. @see example.drushrc.php. Optional.
 --structure-tables-list                   A comma-separated list of tables to include for structure, but not data. Optional.
 --tables-key                              A key in the $tables array. Optional.
 --tables-list                             A comma-separated list of tables to transfer. Optional.
 --target-database                         A key in the $db_url (D6) or $databases (D7+) array which shall receive the data.
 --target-db-url
 --target-dump
 --target-remote-host
 --target-remote-port
 --temp                                    Use a temporary file to hold dump files.  Implies --no-cache.