The reason I actually noticed it was because I was clearing up some useless junk just a few days ago and I remembered the quota being about 3GB. Hence I was pleasantly surprised.
A little googling revealed that Google has decided to increase the storage quota to 6GB by January 2008. Cool! And talk about good timing: I have just (finally) decided to use Gmail to handle my academic (MMU) email since [1] there seem to be lots of problems with the official Webmail interface, [2] I need to store my mails somewhere (I have accumulated 1607 emails since June 2006) and [3] my hard drives (internal AND external) are as full as my stomach after an all-you-can-eat buffet (^^;).
Now... I wonder which is bigger? Yahoo Mail's "unlimited" or Gmail's "infinity+1"? Well, I don't really care, as long as I don't get any "your mailbox is full" warnings (^^)