I recently gained access to some new features in Gmail that I didn't have available to me before - because I was British.
Now that I claim to American, I can access new features in Gmail such as integrated chat (Google Talk), and even a Delete button. If you're currently set to use Gmail in British English you're probably also missing out on these new features. Set your language to American English and magically they'll appear.
As nicely implemented as the integrated chat is, I found that I would often leave a Gmail window open at work whilst I was out of the office. By doing that, it would accept incoming messages for me before they could reach me at home or on my laptop, meaning that I may not see messages for a day (or actually, in this case, a whole week whilst I was in Canada). Because of that, and my tendancy to carelessly leave various copies of Gmail open, I decided to switch the feature off.
One of the things about the integrated chat is that it logs the messages you send and receive through it, allowing you to search it at a later date. If I was using the integrated client, that would be a very handy feature, an extension of my memory, as Gmail already is (and as del.icio.us is).
What I didn't realise - until today - is that messages are still logged in my Gmail even if I use a separate Jabber client (like Gaim, for example). In my Gmail. That's sort of worrying that this remote service is sitting there, unbeknownst to me, recording my conversations. Admittedly, it is very useful, but it certainly shouldn't do it by default.