Editors' note, June 18, 2014: Updated with mentions of the app's newly added star ratings and support for custom sort order, which Adobe added in conjunction with the release of Lightroom mobile for iPhone.
Are you among the Lightroom faithful who've been waiting (and waiting...and waiting...) for a mobile app to allow for remote and lean-back image processing? Well, Adobe's official Lightroom companion app has finally arrived. And while it's not quite all it can be, it should satisfy many of the users who've been waiting patiently.
To be clear: this is not a standalone app. It requires the desktop software for ingesting full-resolution images. It also lacks many of the organizational tools and full-resolution previews that you can get in another Lightroom companion app like Photosmith, but in exchange you get much more responsive performance and a solid set of adjustment capabilities.
Lightroom mobile (LRM) is "free" with any of Adobe's subscription programs that include Lightroom except for Creative Cloud Enterprise -- there are technical issues holding back that implementation at the moment. It requires Lightroom 5.5, which became available concurrently with version 1.1; you can try them both out in conjunction with the 30-day free trial of Creative Cloud if you're not yet a subscriber, or get a 30-day free trial of the app with the perpetual-license update to 5.5. For the moment, it only operates on an iPad 2 or newer running iOS 7.
Aside from its annoying push toward subscription software, there are seemingly valid technological reasons that Adobe LR mobile requires the latest, cloud-savvy versions of its software. It uses the Smart Preview proxies that debuted with LR 5 and syncs them between desktop and mobile using its cloud servers. Unlike Photosmith, which requires both the app and LR desktop (LRD) to be on the same network to sync, LRM only cares that you're connected to a network. Unfortunately, you can't connect peer-to-peer in the absence of a network.
Synced collections don't appear in your regular Creative Cloud file view. Instead, Adobe created a lightroom.adobe.com subdomain where you can view them, and which will presumably acquire more features over time.
In order to use LRM, you login with LRD and enable sync, then set specific Collections to sync. It automatically generates the necessary raw proxy images, though it doesn't indicate within LRD that there's a Smart Preview in the usual spot beneath the histogram. As long as you're connected to a network, the selected Collections and any operations you perform on the images within are automatically synced between the two. If you want to be able to work on images while disconnected from the network, you have to enable offline editing; otherwise, it dynamically downloads each image as you open it and caches it temporarily.
The images are small enough that you don't have to wait inordinately long for them to load, but as a group they're big enough that they can take up a lot of space on a limited-capacity iPad. (Pity that amazing compression algorithm from HBO's "Silicon Valley" doesn't really exist.) You'll probably want to come up with a syncing strategy to manage your storage. The syncing itself happens pretty quickly and seamlessly, at least over Wi-Fi, though there is a noticeable pause before the interface becomes available as you wait for the proxy to download when working online. And you can work on already-downloaded images while it continues to sync.