If I had to summarize the changes in this version of Acrobat in three words, I think I'd go with "work flow enhancements." Every change in Acrobat XI seems to be designed to move PDF files through your hands faster, increasing their interoperability with other applications, and making them more easily accessible from any device.
One of PDF's mixed blessings as a format has always been its uneditability. While immutability means that the file always looks the same regardless of viewing platform or system configuration, it's always been frustrating that you couldn't make basic changes to a document without returning to the originating application.
But now you can; you can edit and add text, perform search and replace, and individually replace images and graphics extremely easily. You're still relatively limited by the page layout -- text will reflow, but if you extend pass the existing area it will overlap with other page objects -- and it will substitute fonts rather than rendering a close-looking facsimile (because, well, DRM). But as someone who routinely has to pull PDF files back into Illustrator for small tweaks based on other people's feedback, I'm chair dancing. The Typewriter tool has been replaced by a full-fledged text engine, and it's faster. If you regularly grind your teeth waiting for the Typewriter tool to load, it's probably worth the upgrade cost. In fact, the program feels a lot faster than Acrobat X overall.
There's also better interoperability with other office applications, most notably PowerPoint. You can export a PDF-formatted presentation to PowerPoint and it makes an attempt to convert text and objects to their PowerPoint counterparts. It will even create slide templates based on your background formatting. With the beta I tested the results were mixed, but usable overall.
Adobe bills this Acrobat update as "Acrobat XI with new Cloud Services," which for the most part means increased integration with last year's acquisition of EchoSign and year-old FormsCentral, plus the ability to access and check in and out documents from SharePoint/Office365 and Acrobat.com resources. It uses EchoSign for managing signature flows and providing audit trails.
FormsCentral desktop comes with the Pro version and in addition to form creation and data gathering now allows you to view response data and generate a summary report, as well as export data to Excel. It's also a lot easier to get started using an existing PDF form, which it can now import, and it's pretty easy to create the linkages between the form and the online data capture.
For organizations that use thin-client platforms for remote operation, such as Citrix, it now supports running the full version of the program off the server, and if you're running it that way on a mobile device it will automatically translate the interface to support touch gestures and space out the icons for fat-finger relief.
Security options have been surfaced, with more streamlined operation. For instance, now it's faster to simply password-protect a file against editing (Restrict Editing) and the ease of redacting information should thrill those responsible for information purges. With one click you can strip out tons of metadata and linked content as well as flatten and purge the file of cruft. I would like the ability to select which data gets purged in the Sanitize Document process, though; for instance, I could imagine that for print production I'd like to keep the metadata and hidden layers, but drop the rest. Sanitize Document is intended for security -- a similar operation for Preflight, which is still really complicated, might be nice.
Adobe Reader gains the ability to access documents from the aforementioned cloud, commenter markup, and simple signature handling (via EchoSign) and the mobile version is now optimized for touch operation. (A beta of the latter was not available to test.)
Acrobat Pro costs $449 ($199 upgrade), while Standard will cost $299 ($139 upgrade); of course, the latest version of Reader will be free to all. Adobe Creative Cloud subscribers will automatically receive Pro, but the subscriptions to EchoSign and FormsCentral require subscriptions on top of that -- at about $15 per month each -- for anything more than the most basic capabilities.