How bad is "Powered by vBulletin" for SEO?

Yes, Here's how-to do it in forumdisplay

Open forumdisplay template, Then find :

HTML Code:

<div id="pagetitle" class="pagetitle">
    <h1>{vb:rawphrase forum}: <span class="forumtitle">{vb:raw foruminfo.title}</span></h1>
    <vb:if condition="$foruminfo['description']"><p class="description">{vb:raw foruminfo.description}</p></vb:if>
</div>

Replace it with

HTML Code:

<!--VBSEO_RR_1--> 

That explains it all. Now I see it

Thanks again!

Great!, You're welcome

Code:

<h1 class="relevant_replacement">[forum_title]</h1><p class="relevant_replacement">Below you will find a list of discussions in the <b>[forum_title]</b> forums at the [bb_title]. The [forum_title] forum [forum_description]</p>

Is the third [forum_title] really necessary? It becomes very repetitive when I check it in my own forum.

No, you can remove it.

Marco, I see you dont have the forum descriptions below each forum here in vBSEO. Should I remove them too in my forum and how do I do that? Hope you understand what I mean.

If you mean that in the forumhome page we don't have the forum description, That's a vBulletin option.

vBulletin options > Forum Listings Display Options > Show Forum Descriptions in Forum Listings set it to No

Is it good for SEO to remove the forum descriptions?

You will hide it only in forum home but the description will site exist in your forum, It's just make the forum looks good than have it but it's don't effect on forum SEO.

If it dont affect SEO at all I will keep them.

Yes, That's as you like.