In March, Google introduced an online version of Google Talk that extends the limited features previously available in Gmail. Yahoo didn't want to give yet another competitive advantage to Google, so they integrated the IM into Yahoo Mail and now offer a standalone version of Yahoo Messenger for the web.
Like Google Talk gadget, it's built in Flash, each conversation opens in a new tab inside the same window, you can find a contact and see his status. Yahoo's web messenger saves all your conversations and makes the history searchable from the same interface. Google Talk saves your conversations from any client, but the history is only available in Gmail.
While Google Talk's gadget is compact and can live inside your personalized homepage, in a new window or in your browser's sidebar, the new Yahoo Messenger for the web adopts the Meebo style of occupying and entire page. If you don't trust third-party clients like Meebo and most of your friends use Yahoo Messenger or Windows Live Messenger, the new interface can be useful when the desktop client is not installed or is blocked.