1. We find out that Wickham left beaucoup de debts behind in Meryton, and may have been involved in some seductions as well (whether they amounted to anything past flirtation is unclear).
2. We learn by further factual proof that Mr and Mrs Gardiner are good-hearted, useful people and that Mrs Philips is . . . not. She claims to come to cheer the family up, but really she's just running in daily with additional tales about how awful Wickham really is.
3. We are reminded of the Kent contingency – Mr Collins is practically chortling with glee over his ability to pontificate, gossip, and triumph over the Bennets all at the same time, while explicitly indicating how glad he is NOT to have married Lizzy, since the scandal would have caught him up as well. He is full of useful "condolements" like
The death of your daughter would have been a blessing in comparison of this. And it is the more to be lamented, because there is reason to suppose, as my dear Charlotte informs me, that this licentiousness of behaviour in your daughter has proceeded from a faulty degree of indulgence, though at the same time, for the consolation of yourself and Mrs Bennet, I am inclined to think that her own disposition must be naturally bad, or she could not be guilty of such an enormity at so early an age.Hateful man.
4. We learn that in addition to living large, Wickham is a gambling man – and owes at least £1000 in gaming debts in Brighton. (No wonder he fled town.)
5. Mrs Bennet is still more ridiculous than we'd believed. She insisted Mr Bennet come home so as to keep him from fighting a duel with Wickham (as if!), then got upset over the news that he was, in fact, coming home without Lydia – because she quite wanted him to fight a duel. *headdesk*
6. Elizabeth realizes that she'd be only half as upset over Lydia's elopement (the term was still used, even though marriage wasn't part of the scheme) if it weren't for the situation with Darcy. Had she never met him, and had he never proposed in the first instance, she never would have thought about his good opinion – and now she's worried that his good opinion has, in fact, been lost – and lost forever. Woe.
7. Mrs Gardiner expected Elizabeth to get a letter from Darcy – and, as we know from discussions about correspondence in prior novels, correspondence between members of the opposite sex were generally limited to those who were related, married or betrothed – so this is an indication that Mrs Gardiner believes that Elizabeth may be secretly betrothed to Darcy.
8. Mr Bennet indicates his awareness that he has been a failure as a father, and acknowledges that Lizzy was right in warning against Lydia's going to Brighton. He also shows a level of self-awareness in indicating that he's not likely to beat himself up overly long.