I don't, but it doesn't actually matter for the purposes of playing a mod. A few mods have switched over to it now for it's increased functionality, and you don't need an orangebox game to play them. You can even develop for the OB engine if you don't have it. Those of you with just HL2/CS:S etc will notice in your SDK that you can select OB as engine.

Sry if this post is overkill, just wanted to let you know there is zero player base issues with switching to OB, in case you were wondering