I have fiddled with Mozilla's Firefox, looked at Opera. Internet Exporer, which is the main Browser used in the world, seems limited and slow compared to the others. It's only use is that Hotmail is stable within it. I often find my Hotmail account difficult to administer when in other browsers. But, to be honest, I would give up my hotmail account in a heartbeat if I couldn't use it in other browsers. Yahoo and Gmail are both stable in other browsers, so I really cannot see why Hotmail can't be.
The big features for me with Rock Melt is that it is intrinsically interfaced with facebook and twitter. My friends are listed down the left hand side of the screen and my accounts listed on the right hand side. I can see at a glance what is going on in both, so that I am instantly updated. The big plus with Rock Melt is that I can be browsing the web and chatting within Facebook at the same time. Previously, and with any other browser, you can only chat within Facebook if you are actually in your facebook account. No going out anywhere. This really impresses me, because sometimes chatting can be a bit slow, particularly where the person who you are chatting with doesn't have English as their native language.
So I am very much enjoying Rock Melt. It is built on the same Chromium platform as Chrome and has many features in common with Chrome. I suppose the creators will keep up with the features and apps as they go along. They don't want a lot of users but in my opinion, they should be pushing this thing to become a standard.