Steve laments the lack of easy “Incognito” windows in Firefox. I tried Safari as my primary browser for a few weeks when I upgraded to Lion and I really missed this as well. Once it becomes part of your workflow, it’s really hard to go back.
I actually want it to go a step further. I want each new Incognito window to be a full separate session. The tabs within that window would belong to that session, but I could pop open new Incognito windows as desired and each would be their own session. Using this, you could log into the same website under as many different accounts as you wanted to – a killer feature for developers to be sure.
Sidenote: There doesn’t seem to be an easy way to link to a Twitter conversation (tweet + replies). That’s one area where Google+ currently beats Twitter handily. I see folks throwing around links to Google+ conversations all the time (hmmm, Wave?).