Yeah, would be nice in the core. I believe Ian is working on merge script, I've got the basic commands you can use in your control panel's mysql command box tho:
Update posts:
UPDATE ubbt_POSTS SET USER_ID = '387' WHERE USER_ID = '9734'
UPDATE ubbt_TOPICS SET USER_ID = '387' WHERE USER_ID = '9734'
UPDATE ubbt_TOPICS SET TOPIC_LAST_POSTER_NAME = 'AllenAyres' WHERE TOPIC_LAST_POSTER_NAME = 'AllenAyres_dup1'
UPDATE ubbt_TOPICS SET TOPIC_LAST_POSTER_ID = '387' WHERE TOPIC_LAST_POSTER_ID = '9734'
Update Post count:
UPDATE ubbt_USER_PROFILE SET USER_TOTAL_POSTS = '24080' WHERE USER_ID = "387"
Update PM's:
UPDATE ubbt_PRIVATE_MESSAGE_POSTS SET USER_ID = '387' WHERE USER_ID = '9734'
UPDATE ubbt_PRIVATE_MESSAGE_TOPICS SET USER_ID = '387' WHERE USER_ID = '9734'
UPDATE ubbt_PRIVATE_MESSAGE_USERS SET USER_ID = '387' WHERE USER_ID = '9734'
If I am going backwards and using the _dup1 acct instead of the more recent acct, I'll use this to update the name after deleting the other acct:
UPDATE ubbt_USERS SET USER_LOGIN_NAME = 'Scream' WHERE USER_ID = '8986'
I believe that covers it, if I've missed something, let me know