I've used WP 1.5 since it came out (and still use it), but have recently started a 'work-related' blog, and installed WP 2.
One thing I really miss from WP 1.5 is that, when I access the 'quickpost' link in WP2, it now launches in the same window/tab that I am browsing... in 1.5 it launches a new window.
Any chance of NOT overwriting the existing browser window in an upcoming rev?