GMail is introducing POP3 access for users, initially leading most to think that GMail could be used as your primary account, as others have mentioned. What I don't get is why anyone would be quite this excited about it. Let's think about this for a moment.
Initially, the selling point of GMail was the 1000MB (1GB) of storage. Others have matched it, so perhaps this selling point has lost its luster. But what is also lost is that most POP3 users will use default settings, and those default settings remove mail from the server. Thus, introducing POP3 isn't so much a feature offering for the service, it's a storage-saving device.
Sure, POP3 can be configured to leave messages on the server. Have you ever tried that in Outlook, then tried to access those messages again from Outlook running on another computer? You end up downloading the same messages all over again, and since storage is so huge on GMail, it could be quite a download.
I understand that offering POP3 access for free may be a feature to sell GMail as a better competitor to other web mail services that don't offer it for free, and I also understand that having a free POP3 account my have some usefulness. But in the end they are two different markets. There is no room for a single conversation that contains both the immense size of the mailbox and the POP3 access to it, since those things don't work together. Now if they were to introduce IMAP, it might be interesting.
In the meantime, I don't think this is so much a selling point to new users as it is getting existing users to switch from the web-based interface (requiring not only extra storage, but cycles to serve those pages, processs searches and the like) to the POP3 one. And can you imagine what will happen the first time a longtime web user tries POP3 and downloads their 475MB of messages, so that they are no longer available online? Oops.