Hi all, just jumping in to say I'm experiencing exactly the same, with Wacom Bamboo Pen & Touch (CTH-670 if that's relevant).
The behaviour outlined above, which appears to be just a delay before the cursor 'recognises' I'm doing a drag select, gives the result that the first few letters of your selection get ignored. Seems to always be the same number of characters (5) that are ignored, regardless of how carefully I click / how slowly I drag.
For a while I thought it was the Windows 8 'hold pen click so it turns into a right click option', as that seems to give me this same delayed drag problem system wide when it's enabled, but that was the first thing to get disabled. So now dragging around the system is fine with that off, but ST2 still gives us the delayed drag issue.
Just while I'm writing and testing this though, I notice that when drag selecting text elsewhere in Windows, the selection highlight will not actually begin until we've selected more than those 5 letters (at which point all other windows programs 'snap back' the highlight and begin the selection at the correct place.
In other words, I'm unable to drag select less than 5 characters at a time in Windows.
At that, I'm inclined to think this is a Wacom / Windows issue at play here, but I'll post this here in the hope it helps someone.