Bonnie Vasko has already posted a brief summary of Wednesday night’s “inaugural” Philly WordPress Meetup, so I thought I’d simply take a moment to document some of the resources we talked about in the “advanced”/developer session. Hopefully some of the other attendees will find them useful.
We talked briefly about

• Free theme frameworks/parent themes, such as Thematic, Twenty Ten and Hybrid
• Commercial theme frameworks such as Genesis, Headway and the Woothemes offerings
• Hooks and filters and their uses in a custom theme (see here for a nifty app outlining all the hooks in WordPress)
• Justin Tadlock and Ian Stewart as must-reads for theming information in general
• Parent and child themes* (separate links!)
• Securing your WordPress installations
• Selling your WordPress themes
• e-commerce using WordPress and, potentially, Magento
• Caching using WP Super Cache, though I have recently taken to using a combination of Hyper Cache and DB Cache Reloaded
• WP Tavern, the WP.org forums and #wordpress/#wordpress-dev on freenode as destinations for those seeking more online WordPress community opportunities

I’m sure there are some other things I’m forgetting to mention, so if anyone has anything more to contribute (or further questions), please just drop a comment.
I’m looking forward to the next meetup!