The built-in Google Talk client in Gmail has added an "Invisible" option to the status dialog, letting you appear offline or unavailable to other Gchat users, but able to see who's online and start a conversation under the radar. The feature doesn't appear to be available in Google Talk's standalone client, and, in fact, signing into Talk will nix your stealthy status if you've got Gmail open simultaneously. Seems like a good way to keep distractions at bay (or at least be distracted only when you choose). The "Invisible" feature is only available to users of the new Gmail interface. For more chat-when-you-want-to control, check out a tool to auto-set your status to idle when busy.