Vertex slide past edge limit? The first Vertex Slide tool took an additional click, but you could push the vertex beyond the end of the edge. Is there a setting or method to achieve that with 2.68?

The old method of placing the cursor at the opposite vertex and scale away from it is wonderfully nostalgic, but a bit time consuming.
Yes, by using the Clamp setting.

Access by holding Alt, or toggle with C. This allows you to slide past the (0-1) limit and also prevents switching to slide along other edges then the ones currently selected.

This information is available in the header text during vertex slide.