We are polishing the last details before starting the Bugzilla migration to Phabricator on 21 November at 00:30 UTC.
http://www.timeanddate.com/worldclock/fixedtime.html?iso=20141121T0030
You can find all the details of what will happen next in the timeline at
https://www.mediawiki.org/wiki/Phabricator/versus_Bugzilla
MIGRATION WEEKEND
Basically, Bugzilla access will be restricted to read-only, Phabricator will be pulled, and we will start the migration. If all goes well, by Monday 24 Phabricator will be back with about 75k tasks, and Bugzilla will be archived in old-bugzilla.wikimedia.org.
During this period, we will redirect users to a page asking them to postpone their bug reporting unless it is so urgent that it cannot wait until Monday. In that case, they can use #wikimedia-bug2phab on IRC and mediawiki.org's Support Desk.
If you registered in https://phabricator.wikimedia.org before the migration, your Bugzilla activity will be probably assigned to you by the time you check the site. Otherwise, you will still be able to register and claim your activity, which will be assigned to you within a couple of hours or a couple of days, depending of the queue.
KNOWN ISSUES
We are confident about the stability of Phabricator and also about the reliability of the migration process. However, there are several known issues related with data and features that will be missing next Monday.
We cannot assign to Phabricator tasks the same number as their Bugzilla equivalents. Instead, automatic redirects will link old Bugzilla URLs with their corresponding new Phabricator tasks. phabricator.wikimedia.org has already >1300 tasks with numbers taken. The migration needs to be done by batches of bugs instead of sequentially, which makes the mapping of numbers more complicated. Still, smaller numbers will correspond to older bugs, and we will do our best during the weekend to improve the sorting.
Votes and saved searches cannot be migrated. Users willing to have their equivalent in Phabricator (tokens a new saved searches) will be able to access their accounts in old-bugzilla.
A feature that we expect to be missed is suggestions for duplicates when creating a new task. Even if Phabricator's search is powered by Elasticsearch, we feel like it needs some fine-tuning to get to Bugzilla's efficiency. Advanced Bugzilla users will also find that some actions take more clicks (assigning blocker/blocking tasks, for instance). In general, most fluent Bugzilla users new to Phabricator will need a few days to get used to how things work in Phabricator.
There is a complete list of known issues at https://www.mediawiki.org/wiki/Phabricator/versus_Bugzilla#Known_issues -- and we will keep working on them after next Monday.
IMPROVEMENTS
We expect that the improvements will make the change worth right after the migration, of course. A simpler and cleaner UI that works on mobile, Wikimedia SUL, bugs and features living together, ability to associate tasks to several projects, workboards, and many more features are waiting for you! :)