The features being trialled are very much experimental; many (such as the Snake game) are unlikely to actually make it to production, but will give the Gmail development team some serious critical feedback and data on how users use their Gmail. Gmail Labs is still being rolled out to English users; it will simply show itself when ready.
This approach is quickly gaining popularity among the web development industry; Google is in essence inviting its few but most reliable users – the tech-savvy bleeding edge early-adopters – to run a broad end-user test from which the team can quickly work out what should make it into the core Gmail app. Gmail’s user base is very suitable for this, but even a quick message displayed to all users inviting them to join a beta test can identify a suitable cross-section of your user base.
Gone are the days of assembling elite teams of average end users or hiring professional agencies to conduct testing – just putting the features out there and inviting users to take them for a spin (and keeping an eye on them as they do) is the 2.0 of beta testing for proprietary applications. Open source projects have had public bug trackers for a while, and are generally effective in their beta testing, but the approach is inhibited by the user needing to take the initiative to submit a report. Access to the user while they interact with the application is the crucial aspect here; only SaaS can pull it off, and Gmail has done so masterfully.
So the next time you want some users to try out a feature, just hide it in a profile page or an account settings area, and quietly let your users know. Blog posts work great; the minority you’re aiming for are right within the group that would subscribe to your RSS feed. Let your users take care of the rest; transparently log their interactions with the features to see what they find useful and what they don’t. (External debugging suddenly makes a lot more sense when you know exactly what led to the problems.) Quite literally, “watch and learn” – this is beta testing evolved.