Every week, the WordPress core developers get together to discuss a series of items that are outlined on an agenda. This agenda is not set in stone and in fact, users can suggest topics to be discussed at each meeting by suggesting them on the agenda outline posts on the WordPress development updates blog. For example, Jane is currently taking submissions for items to be discussed during the July 22nd meeting which is this Wednesday. So far, meta tables and committer workflow are on the table. If you are a plugin or theme developer and have something you want to discuss being added or reworked, I suggest trying to get it on the official agenda for the meeting and then showing up to talk about it. These meetings are where a good chunk of decisions happen which shape the direction of the WordPress software.
So how do you join the chat? Developer chats are held each Wednesday in the IRC channel (irc.freenode.com #wordpress-dev) at 9 PM UTC (5pm Eastern, 2pm Pacific). However, there is talk that the time and day might change. For the July 22nd meeting, it will be at the normally scheduled time.