From the Google Docs email newsletter:

If you have an iPhone, Blackberry, or Windows Mobile device, now you can point your phone’s browser to http://docs.google.com/m to view read-only, mobile-optimized versions of your docs and spreadsheets. (Your presentations, too, if you have an iPhone; we’ll be making this feature available for other devices shortly.) You might have to squint a little, but now your information will always be right there, in your pocket, wherever you go.

The interface only allows viewing. You cannot edit your documents, spreadsheets or presentations, but just being able to access all my Google Docs is enough for me. I don’t need to edit my documents through my mobile phone - I have a laptop for that.