The ridiculously popular Mailbox app is now available for anyone with an iPhone. When it was first released the developers implemented a queue system. They realised just before release that their servers were going to be overloaded, to limit the strain on their servers they only gave the app on a first-come-first-serve basis. Some people were hundreds of thousands behind in the queue because it was so popular.
With the popularity of Mailbox, big names noticed, so they got snapped up by Dropbox in no time. Dropbox have the resources to take Mailbox to the next level and that's what they're doing now by letting anyone and everyone download and use Mailbox. With Dropbox now owning Mailbox they'll easily be able to handle the resources needed and can scale quickly.
Check out my review of Mailbox if you haven't already. All we need now is Mailbox for the desktop.