Does anyone know if openbsd has an official support cycle for their releases? Ie, if I install the new 4.6-release today when will I stop getting patches via the -stable branch?

As I understand it, they provide patches for latest release and release - 1 , so you'll get 12months worth if you install a new release right when it first comes out, or around 6-7 months worth if you install just before the new release is cut.

Isn't that a little short? Are bugs/issues at least reported (as opposed to patched) for longer? I ask because I have several openbsd wireless access points left by a predecessor at my new job running openbsd 4.1, and I'm wondering if I should upgrade them. The errata for 4.1 only shows patches up 4/3/2008, as you described. How do I know if its safe to keep using old releases?

Correct. This is covered in Section 5.1 of the official OpenBSD FAQ:

http://openbsd.org/faq/faq5.html#Flavors

Support for OpenBSD 4.4-stable ended with the release of OpenBSD 4.6-release which was yesterday.
This is the established policy. Unlike Linux, the OpenBSD project is quite small, & resources are required to support old versions. The project developers consider that other issues are more important.
Perhaps; maybe not. I haven't taken the time to look at the bug database to verify this conjecture one way or the other.
Correct. Support for OpenBSD 4.1-stable ended with the release of OpenBSD 4.3-release which occurred 1 April 2008. New releases of OpenBSD occur every six months. The project has maintained this schedule for some fifteen years.
How you define "safe" is up to you, but I would say that the importance of patching & keeping systems up-to-date should be proportional to the importance, sensitivity, & timeliness of whatever is being protected.