Google is making the best of allowing enthusiasts and 3rd-party developers early access to the next release of Android, and the result will be a less buggy release when L finally hits the grand stage. While new issues are reported each day, there's a lot of progress showing up on the Issue Tracker. Just yesterday, a burst of 18 bugs were marked as 'fixed,' following a 2-week gap without any obvious activity.
Among the many fixes, both major and mundane, we can see a lot of attention has gone to the networking and wireless protocols, sensor-related problems, and a fair number of visual tweaks. Certainly the most notable of the recent fixes is an issue where tethering (Wi-Fi, Bluetooth, and USB) ceased to work for a number of people. Other networking issues that got the nod include a problem with routing traffic through proxy servers (a necessary aspect of using VPNs), an inability to set a static IP on Wi-Fi networks, and some assorted Bluetooth issues.
Some of the reports might also give us a hint about things to be on the lookout for in the future. One user brought up an issue where an app could stop receiving touch events after the Pocket app drew over top of it, suggesting that there might be some changes for security or stability reasons. Another details how services can be killed too readily, even when apps are currently bound to them. The proper handling of services has long been an issue in Android, even gracing our Bug Watch series, so we should expect to see some behavioral changes (and new bugs) as a result.
There are about 1100 reported problems on L's dedicated issue tracker. (Actually, it's 1400, but 300 of those have been marked as duplicates.) So far, only 58 have been marked as fixed, with a little over 200 listed as closed, invalid, done, or "wontfix" for various reasons. In all, that leaves about 850 reports that are hanging open in various forms. The Android team certainly still has a lot of work ahead. Since this is such a major revision to the OS, both visually and functionally, there are bound to be several unpleasant surprises here and there; but exposing a preview release to a technically skilled audience is proving to be an excellent way of weeding out the real problems before they hit the open market.
Source: Developer Preview Issue Tracker