Now search giant Google offers a new service in Gmail, which will help us to view the Chat(text) conversations inside Gmail.
The chat logs can be viewed & searched, like emails and also it can be sent as email. Even we can move the message to Inbox, we can add a star etc. This new feature of google has to be enabled to before use.
So I enabled it few hours before and tried to archive it. Its cool 
In my Google Talk (gmail) account, Im connected to very few people, & hence im not using it often. But I can say that its very simple & low resource hungry application when we compare it with Yahoo Messenger & Hotmail.
I used to save all the Chat conversation in Yahoo. The main difference between both is : In google, the chat conversations are stored in Gmail Account, and in Yahoo it is stored in the PC where you are using the Messenger. So, we have to enable archiving in Yahoo each time we re-install the messenger / we loggin in different machine. Also in Yahoo its is saved in Profiles folder in Yahoo installed directory with a .dat extension and its encrypted. The best about Yahoo is you can send offline message, but not in Google.
Update : Now Google Talk supports Offline messaging, which is also saved in the Gmail.