There's probably some reason why I didn't use OnUserSave to begin with, though I can't remember what it is.
The Subscribe snippet actually acts as a posthook for Register, so you should be able to use the &usergroups property in the Register tag of the sbsRegisterFormTpl Tpl chunk.
IIRC, the format is:
&usergroups=`usergroup1:rolename,usergroup2:rolename`
The role is optional, so it could also be:
&usergroups=`usergroup1,usergroup2`
or just:
&usergroups=`usergroupname`
By default, it puts all users in the Subscribers group with a role of Subscriber.
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