Maybe you don't want to show full names associated with the comments in G2, but show usernames instead. Unfortunately the module doesn't allow the ability to choose yet, so I had to hack the files.
In the file gallery2/modules/comment/templates/Comment.tpl go to the last few lines
<p class="info">
{capture name="date"}{g->date timestamp=$comment.date style="datetime"}{/capture}
{if $can.edit}
{g->text text="Posted by %s on %s (%s)"
arg1=$user.fullName|default:$user.userName
arg2=$smarty.capture.date
arg3=$comment.host}
{else}
{g->text text="Posted by %s on %s"
arg1=$user.fullName|default:$user.userName
arg2=$smarty.capture.date}
{/if}
</p>
I changed $user.fullName to $user.userName. Dunno what the second portion after "default:" is for.
Additionally, if you want to change the item owner's fullname to username, in gallery2/modules/core/templates/blocks/ItemInfo.tpl
{if !empty($showOwner)}
<span class="owner summary">
{g->text text="Owner: %s" arg1=$item.owner.fullName|default:$item.owner.userName}
</span>
{/if}
Change $item.owner.fullName to $item.owner.userName
More info in this forum thread