The love between Yahoo and Google has grown beyond the search deal and now they are connecting their Instant Messengers. In a press release statement both the companies "agreed to enable interoperability between their respective instant-messaging services, bringing easier and broader communication to users". This means that you can chat with Google Talk friends from Yahoo Messenger and vice-versa.
Already Yahoo & Microsoft enabled interoperability between their messengers that allows Yahoo users to chat with Live Messenger users and vice-versa. Similarly Google Talk and AIM users can talk to each other.
So if you have more friends in Yahoo, Live & Google Talk Messenger then Yahoo is the best messenger to stay connected. If you have more friends in AIM, Yahoo and Google Talk messengers then Google Talk is be the best messenger to stay connected.
This is a good move towards interoperability of Instant Messengers.
By the way is your work place or university blocked the Instant Messenger access? Here is an excellent from Tech Dreams to unblock and access the messengers.