ac_no_dc said:
I don't know if there's a limit to how many you can have, but I do know there's a limit to how many you can add at once.
I believe the limit is around 4000 characters total, same as the My Tags list, but because of the site's programming language each single blank space counts as 5 characters towards the total.
ac_no_dc said:
There have been times where I added about 20 odd tags at once, logged in the next day and found they were all gone.
Blacklist and My Tags lists are saved in the cookies on your device, not on-site, so anything you add while in Incognito/Private Browsing mode doesn't get saved when you log out.