GoodThings2Life & Jakobimon: I think you're being a little quick to pull the trigger judging Outlook 2013's whiteness based on the preview relased so far. This is good feedback which will be considered for the final RTM release.
James: Exchange ActiveSync will continue to be the most frequently used way to access Exchange mailboxes from tablets and phones for now. It has offline sync which is important on unreliable mobile networks, whereas OWA for tablets and phones (for now) is an online only experience. OWA for tablets and phones is a great quick way to access your mailbox from someone else's tablet/phone, and it offers a set of functionality which most EAS clients don't (e.g. seeing lots of information from the Global Address List and other sources about a person; meeting scheduling).
Karsten: single-line view is not in OWA2013. But thanks for the feedback. We'll consider adding it for future releases.
Karsten & Nuno: We have prioritized showing data other than email size about messages since we, since E2007, see most customers deploying Exchange with large mailboxes (at the very least 5GB). Managing messages based on size has become much less important to most users today, compared to 5-10 years ago.
Paaja: Unfortunately we don't offer OWA Premium on Android with Exchange 2013 RTM. But given the market share of that platform, we have it on the investments we are considering for the future.
Andy: OWA supports display of data from multiple mailboxes today (even with Exchange 2010). This is called "aggregation". It sucks all the data from another mailbox into your primary mailbox, so you can see both when looking at your primary mailbox. OWA also supports userA looking at userB's mailbox directly (this is called "open other mailbox" in the OWA UI), but when doing this, you can't see multiple mailboxes in the same OWA window.
Wlodzislaw: I think you're commenting on the new outlook.com service here, which is not the same product or UI as Outlook Web App (OWA) which this blog post is about. OWA only works against MS Exchange accounts.