I've created a smooth path around an image that I'd like to vectorize. Now I'd like to fill that path to make it a solid with smooth edges.
The path is filled, but the lines are jaggy. What am I missing in order to make the edges smooth and crisp - i.e. vectorized?
Filling a path can make slight "jaggynes". For the pixelation goes, it all depends on the resolution of your document, remeber that photoshop documents isnt vectorbased in the same fashion that Illustrator, and that you cant get the same scaling.
When choosing the path tool, make sure to chose the shape tool in the drop down menu. 
When using the Path tool to create a path, a popup button in the options bar dictates if it will create a path (shown in the paths panel), or a shape layer. If you’d like to create a filled shape, this should be set to Shape.
If you created a path instead, that’s okay. You’ll know you’ve done this, because the paths panel will show an item called Work path.
Choosing Layer → New Fill Layer → Solid Color will create a solid fill shape layer using the path you’ve just created. If the result is the inverse of what you’d like, choosing the Combine Shapes from the boolean menu in the options bar will fix it.
In Photoshop specifically, you need to use the pen tool to create vector shapes. You can also use the shape tools and choose a fill color. The marquee tools (i.e. lasso, rectangle, circle or magic wand) will always have a pixelated edge when zooming in. If plan to work exclusively with vector shapes you will want to work with Illustrator.
Select your path, then in layer panel in lower right corner select create new fill/ adjustment layer and select solid color.
I also had this problem, but the answer is really simple. You just have to tick the Anti-alias option under the Feather Radius in the Fill Path window.
I think you are confused with path and shape. If you work with shapes you can add fill and/or stroke as you want with pixel-perfect results. Paths are commonly used for masks, cut-out paths and similar. Try to convert your path into a shape and then edit from the top menu as indicated in image. Check also the adobe help about drawing shapes.
I found this because I am having the same problem....haven't tried it yet, will do first thing in the morning. I hope this helps you too....hope it works!
The best is using Illustrator and copy paste to Photoshop as smart object. Any editing done in Illustrator will be real time update in photoshop.
