While this might look cool there is another side to this story, people can actually see when you are reading your Emails on your Gmail account.
I, for example, use GAIM as my main IM client and since Google Talk (GTalk) uses Jabber as its underlying protocol, it means that every Jabber supported client can connect to GTalk. Jabber has built in support to show your status and the client you are using and most Jabber clients (besides GTalk) allow you to see this text.
Google Talk’s integration within Gmail is implemented in such a way that Gmail is converted into a Jabber client. The engineers at Google Talk used the client text and it clearly shows “gmail” in it (as opposed to Talk.vXXXX that is shown for GTalk clients).
Since the option for having the Chat integration is turned by default, if you use a client that is different than GTalk (like GAIM) one can see exactly when his/her friend is inside Gmail.
What do you do when you are in Gmail? Probably reading (or at least seeing) Emails.
A bit annoying isn’t it? I don’t want anyone to know when I’m actually logging into my Gmail account and read/see my Emails.
Luckily you can turn this off. There is an option at the end of the page after you login into Gmail that says “Gmail view:”. In there you can select “standard without chat” which will turn off the GTalk integration.