Google are aware of the problem and seem to think that it will be back for pretty much everyone with the next few hours.

It still seems to be working on my iphone but the web interface is the thing that seems to be fooked!

**Update**
Bellow linked is a mashable article containing a statement issued by Google regarding the 1st of September Gmail outage. (The gist of it is that Google took out some servers to do a routine upgrade and their routers got fed-up with too many requests, went for a beer, got drunk and fell over)

Google: Gmail Outage Was Our Bad