Emailing Gabe directly was helpful in getting a WINE issue debugged in the days before native Linux support (actually turned out to be a Linux kernel bug). I don't want to encourage people to spam someone whose time is surely scarce, but perhaps if all other avenues are exhausted and the stakes are high, this may be a reasonable approach.
By the way- for security issues, their security@valvesoftware.com address gets /very/ fast, human replies. For example- when Steam Curators rolled out, you could use javascript: URIs for links to "read full review". 5 minutes after Curators was released to the public, I discovered that. 30 minutes later, it was fixed.
That said, that's just their web app; getting issues fixed in games is MUCH slower.
