It's very fast, compared it last night to my father's Eris default Browser and most pages rendered much faster (both on WiFi). Some pages that were kept simple, like my work's website (minimal graphics, zero ads and no flash) came up simultaneously.
Opera presents the text already aligned to be zoomed in on. I like this because on the Eris the default browser has to realign it when you try to zoom. I like that it keeps you from needing to side scroll (default browser) but it lags if the phone isn't fresh from a reboot. Opera keeps it nice and speedy all day long, and going back to previous pages is super fast. I like the trackball feature when zoomed out, if you get it close to a block of text, it's pretty good about figuring where you wanted to go and zooms on the block of text.
It has a few things I don't like, text is really rough and basic, hoping for some options later on. Also noticed signing in took a few tries to get it to go, but once you get signed in, things fly. It's still in Beta, will be keeping this and looking forward to new features later on.