When is the next update?
The developers decide on a set of goals that will define the next release. Some of these goals (usually bugfixes) are mandatory, and the release will not occur until they are fixed. Some (usually features) are just goals, and may or may not show up in the release they are targeted for.
Although we very rarely set a specific date for a future release, you can get an idea of how far away the next release is by viewing the latest release tracking bug. The checklist also gives you a good idea of where you can start if you want to help out.