I just tried to create a ticket in Phab. I understand that the Project field is similar to Component field that we used in Trac. (It's a bit unfortunate that a project can't be further separated into components). However, there's no text completion in that field unless you type in something. There's no list of projects nearby (unless you know which icon to click in Phab and find it in a separate page). I'm a bit afraid that people won't be able to report bugs in Phab unless it's easy to find "taskotron" or something through the Project field.
Sure, I assume we can provide custom URLs which fill in the project field through GET arguments, but then you need to spread these links everywhere so that people don't find a different way to the system.
Am I missing something?