Getting all entries posted on any given weekday Super simple request, not sure if it's possible...

Can we pull all entries that were posted on a Monday, for example? Or pull all entries but group them by the day name they were posted on?
Can't think of a way how to query posts from a certain day, but you can certainly group entries by day they were posted on:

{% set allEntries = craft.entries.section('blog').limit(null) %}
{% for day, entries in allEntries | group("postDate|date('l')") %}
    &lt;h2&gt;{{ day }}&lt;/h2&gt;
    &lt;ul&gt;
        {% for entry in entries %}
            &lt;li&gt;{{ entry.getLink() }}&lt;/li&gt;
        {% endfor %}
    &lt;/ul&gt;
{% endfor %}