Timber is a general-purpose error-logging and alert system for WordPress.
Maybe. There are several things that could wreak havoc when installing Timber on a live WordPress site, and it's important to understand what they are. As a start, follow these two steps:
1) Don't log Notices or Strict messages. The average PHP script, even the well-written ones, commits several "minor infractions" on every execution. This includes many of the scripts in the WordPress core. If Notices or Strict messages are enabled for logging, it will result in many multiple errors logged each and every time any user loads any page of your site.
2) Keep an eye on your logs for awhile. Even with Notices and Strict messages disabled, some themes or plugins may generate a number of Warnings or other error types. Since these will be logged every time the offending page is loaded, the logs may still fill quickly depending on your site traffic. If this starts to happen, you'll want to disable logging entirely, or clear the logs regularly.
Clearly, the main concern is the logs filling too much or too fast. Why is this a problem? Timber logs errors to a custom table in your WordPress database. Your database very likely has a space limit on it, the size varying dependent on your web host. This available space is already partially filled by your posts, comments, and other WordPress data, as well as any custom data stored by other plugins. If the space runs out, your site may become inaccessible. In addition to the space limit, many database configurations have a limit on the number of connections or data operations. If a single page generates several errors, that multiplies the number of database calls for that page across every user. And if the limit is reached, again, the site may become unreachable.
Timber works best on a development server, as a tool for programmers to track down the bugs in their plugins or themes. It can be useful on a live blog, but make sure you understand the uses and potential hazards.
Not at this time. Timber is primarily a debugging tool for developers, meant to trace programming errors to their source. There are several types of "expected" errors that WordPress handles, including those managed by the WP_Error class, that Timber does not monitor. Many of these are not solvable, in the permanent sense - such as an error message that occurs when a user attempts to login with an incorrect password. As such, they would only clutter the error logs.
That being said, there are certain error types, such as 404s, that future versions of Timber would benefit from logging. Feel free to request features and let us know how you're using Timber.
Timber has been developed and tested only on WordPress 2.7. In all likelihood, it will work fine on previous versions of WordPress, although the admin screens may not match the formatting well. One of the goals of the upcoming 1.0 release is to be tested and fully compatible with versions at least as early as 2.5.