Benefits of Yahoo! Mail Beta include:
Drag and drop messages into folders for better organization
A preview pane makes it easier to read your messages
Keyboard shortcuts such as Ctrl-S to save a message
Navigate from message to message with the arrow keys
Messages open in tabs or new windows so you can multitask
Yahoo! Mail Beta doesn’t work in Opera (GMail does), it’s pretty fast, loads faster than GMail, but you don’t have the feeling you’re using a desktop client. For example, scrolling the list of messages takes some time, you have to wait a couple of seconds after you select a message (you only see: “Loading message…”).
The built-in RSS reader works very good, it imports your feeds from My Yahoo, but you can’t categorize them or move them, you can’t expert your subscriptions into OPML.
The Beta Mail doesn’t preview attachments (not even images), it opens any external link in a new window. The tab functionality is really limited: you can use it for searching, composing messages, but you can’t compose two messages simultaneously. I wonder why they implemented the tabs (I know: so you can multitask) if they are so limited.
The shortcuts are really nice:
Check Mail m
New Message n
Print Ctrl+p or p
You can finally attach files easy, but they could remove the Browse and Attach buttons and instead use a Add button next to remove that would combine the two buttons. It would be one single step, a very intuitive list UI, that could be integrated in Compose tab.
Overall, the new Yahoo Mail is much better than the last version, you can’t see (too many) ads, but doesn’t have many features included in GMail (label, fast reply, POP3, forwarding, automatic mail saving, attachment preview), but outperforms GMail with is Outlook-ish design.