Webkit - Nightly Builds

So, the other day, I came across a forum post telling me that this thing called Webkit could double the speed of my Safari browser. A little shady, but with a source coming from Anandtech, I knew I could trust it. I downloaded it, and WOW, The Verge was so smooth.

I have a few questions first though.

What is Webkit?

Is it like a separate application? It has its own icon, etc. Yet, it look exactly like, and I think is, Safari. With WebKit open, opening Safari makes things a little weird.

What's with the daily updates?

It seems like one or two updates of Webkit comes out every day, and each one is 44.8 mb. Why are there so many? Are there improvements in each one? Do I need to download each one? Are the downloads cumulative, or do the 44.8 mb replace the previous 44.8 mb?

Why is GMail's text all messed up?

Every time I use Gmail, the text is jaggy, pixelated, and funny. I have a MacBook Air 2012 13 inch. Is it because Webkit lacks some type of Font Smoothing? How can I fix it? Or is it a bug I have to live with?

How do you set it up as your default browser?

Whenever I open links from say, Messages, it still opens in Safari, causing some strange problems. How do I set it as my default?

Why does it use sooooo much memory?

I feel like I have two Safari's open. Not that concerned about not enough memory (8 gigs :) ), but just curious. In Activity Monitor, it shows "Webkit" and "SafariForWebKitDevelopment Web Content" as processes, each with about the same amount of memory. WHY???