APC 3.0.14 (code named "A bigger boy made me do it, sir") went out a couple of days ago - read the release announcements. The major things in the release is a fair bit of performance improvements for those don't use threads. Also I've figured out a quick way to limit memory fragmentation when APC user cache (apc_fetch/_store) is heavily used - the new fraglimit fixes should solve all the small fragment issues with 3.0.13. And following my recent obsession with drawing pretty graphs for everything, here's how the old version looks compared to the latest code (requests per second for an include_once benchmark).
To get to such levels of performance, the code has some configuration parameters that can be set. The apc.localcache creates a process (yes, not thread) specific lockless cache which is basically a layered shadow cache ontop of the same shm data. The apc.include_override_once is also now usable because of the appropriate checks put in to reduce the overhead of include_once. And now, when you enable apc.stat there's a bit of code which pre-computes the path of the included file so that it can be effective for includes with relative paths or from include_path dirs.
The release is hopefully stable enough to provide someone with enough ramp-up time to get started, if I stop working full-time on APC. I've spent a fair bit of time stabilizing basic functionality and have kept most of these optimisations optional, to be able to look at other work for a while.
--Periods of productive stability, interrupted by bursts of test-bed change is much less disruptive than constant ripples of change.
-- Fred Brooks Jr, "The Mythical Man Month"