For the past few months, I've been living inadvertently in this Mythical Cloud that people have been punting for so long. Yep, good old Gmail. I use it every day via my crusty old Firefox web browser, and the last time I opened up Thunderbird was months ago whilst commuting for a few weeks to the Smoke (on one of those High Speed/No Internet trains).
Google pestered me with their Priority Inbox for a while before I succumbed. Rather like the idea of the cloud (your data is separate, online and accessible wherever [sic] you are), the idea of the Priority Inbox took a while to take hold.
It's actually very simple: Star the stuff that needs further action. The priority stuff (which you can 'train') comes to your attention at the top of the list. The unread unimportant stuff is bold. Read it, star it, archive it. Highly recommended.