Ну и денек выдался в минувшую субботу!
I'm assuming it literally means "my/our little day stood out from others. It was special somehow", but its precise meaning eludes me.
It's been an eventful day. [in a positive sense]
or: It's been a rough day. [with a negative connotation of struggling]
or: It's been a long day. [feeling as if several days have passed in a single day]
On a side note: Is it just as acceptable to say "день выдался"?
"день выдался"
- would sound quite weird and ambiguous. However for positive estimation there can be "День удался" (after the day or towards an evening" or "день задался" in the morning or noon, within the very heart of the day.