I'm going to make a good faith effort, but be forewarned that I've actually never used, SafeCracker Registration.
Modules like Zoo Visitors, etc., give you replacement channel tags, bit from what I can see for SafeCracker Registration, the tags are focused on the registration and editing process, leaving the regular ExpressionEngine tags for handling pulling and looping through data.
So accessing member data would be the same as accessing a channel entry. The SafeCracker Migration Utility, (accessible via SafeCracker Registration Settings, I'd assume), seems to be the area where you'd map information. So if you regularly need to access the member_id number, that should probably be mapped to a custom field. Otherwise, I'd assume that accessing member data would look like:
{exp:channel:entries channel="members" limit="10" orderby="member_lastname" sort="asc" dynamic="off"}
<div class="member-list">
<h3><a href="http://mysite.org/member/profile/{url_title}">{title}</a></h3>
<p><em>Location:</em> {member_location}</p>
<hr />
</div>
{/exp:channel:entries}
Very similar to regular channel handling. Now handling member groups would be interesting, because I can't tell if you can map member groups to categories or not. If you can't you'd probably want to do this on the template itself, as a hidden field, if all members were going into one major category. If members were getting assigned to different categories/member groups, then you may need multiple registration forms or to assign groups and categories after the fact.
Or if you didn't need the other profile data for the listing, you could use the regular membership data tags or a custom query to pull a membership listing by group.
I'm not quite certain what you're attempting to accomplish with the members by member groups. SafeCracker Registration, from what I can tell works best for if you have a simple membership/registration process but want the flexibility of use channels. If you need to assign members to multiple membership groups or do other complex things, then based on the write up on Objective HTML site, SafeCracker Registration may not be for you.
But I can't tell if you needs are fairly simple or very complex.
SafeCracker Registration
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