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