The number of monthly unique visitors for Google's Gmail Web mail application grew a great 43 percent in 2008 to 29.6 million, according to TechCrunch's Erik Schonfeld, cobbled new stats from comScore, and noted:

In contrast, the much more massive Yahoo Mail grew 11 percent to 91.9 million uniques. AOL Mail finished in second place for the year with 46.6 million uniques (plus another 7.2 million visitors to AIM Mail), while Hotmail actually declined 5 percent to 43.5 million.

Google doesn't release Gmail user numbers beyond saying "tens of millions of users." No doubt the proliferation of new tools, including the ability to turn e-mail into Google Docs, a task manager Canned Responses and SMS text chat, are spurring the explosive growth of the Web app.

Schonfeld goes on to suggest that Yahoo may not have to be so scared, but let's not get ahead of ourselves. Who knows what will happen at Yahoo under the auspices of new CEO Carol Bartz? She could turn around and sell the company to Microsoft, or at least outsource its search.

Assuming she keeps Yahoo independent, she must continue to whittle Yahoo's own dark matter, to borrow Google CEO Eric Schmidt's phrase.

With 92 million unique monthly visitors, Yahoo Mail is the e-mail blue whale and clearly not a dark matter casualty. Taking the Yahoo Open Strategy plan to open up Yahoo apps, the future of Yahoo Mail looks promising, but will Bartz stay this course or scrap it?

Meanwhile, even as Google Web services gets lopped off like so much fat from the lean, Gmail continues to roll.

The latest Gmail Labs tool is a "Send & Archive" feature that archives sent Gmail messages so you're inbox doesn't get cluttered.

The feature, which you can enable by clicking the Labs tab under Settings in Gmail, clicking the Send & Archive choice and hitting save, sends your e-mail reply and archives the thread with one click.

Once activated, you'll see the button appear at the top of your message, to the far left of the Send, Save Now and Discard button. It looks like this.

Pal Takacsi, the engineering manager who created the feature, said he'll add undo support, so that when users accidentally archive a thread, they can get it back into their inbox with one click.

I can see how this Send & Archive utility will be valuable to people who live in Gmail and use it as much as a repository for their Web content as a communications tool. Workers who live in Gmail may want to refer back to conversation threads on a regular basis, so one-click archiving is key.