"Rincon" is the code-name for Microsoft Internet Explorer 7.0, expected to ship this year. A lot of what we hear now is motivated by political reasons: the focus on security is a counter-measure against Firefox, which everybody says is more secure than IE (which some in return say is just because it's less popular, so it's less of a target). A lot of things we don't hear of at the moment are actual improvements to e.g. PNG transparency, a fully supported CSS selector syntax, and similar issues which make a web developers life a little harder in today's IE. Some more inside information – tabbed browsing as default? I don't think so – is available at Microsoft Watch:

http://www.microsoft-watch.com/article2/0,1995,1776290,00.asp