Dropbox has announced a major update to its pre-release Experimental Edition backup and sync software. Dropbox Experimental Edition 1.5.27 has been rebuilt using Python 2.7 (the current stable build, Dropbox 1.4.17, is based on Python 2.5).

Dropbox describes the result as “a Dropbox client that is faster to run, and easier for us to develop new features”. By way of example, version 1.5.27 includes a number of major new features, largely aimed at OS X users.

The major benefit of building Dropbox Experimental Edition in Python 2.7 for all users is performance. It also promises improved web logins from the client.

Now Mac users can install Dropbox via its own installer

All other new features are Mac-only: version 1.5.27 comes with new icons that promise Retina support. It’s also bundled with a new, simpler installer – just double-click to install. There’s support for Mountain Lion’s new Notification Center, and a fix for the delay when bringing up the context menu.

As this is the first release of a major new build, Dropbox is keen to stress that issues will arise, and recommends all users intending to install Dropbox Experimental Edition should back up the contents of their Dropbox folders before installing it.

One major issue already noted at this early stage is slow startup times on OS X, which also has an effect on installation times, so users are asked to double-click just the once and wait. Other issues are also starting to be reported by end users – visit the Dropbox forum to get rolling updates on these.

Dropbox Experimental Edition 1.5.27 is available as a free download for Windows, Mac and Linux users with a Dropbox account. Also available is the latest stable build, Dropbox 1.4.17.