Basically, when you access Google Docs in your mobile browser (by visiting docs.google.com), you can view any Word, PowerPoint, or PDF file in your documents list -- no need to download it first. (I was also able to view Excel spreadsheets -- maybe that functionality was already there?)
If this sounds a bit familiar, it's because just last week, Google made it possible to view Word attachments right inside Gmail -- no need to download the files first.
Now for the bad news: you can view documents, but you can't edit them. For that, you'll need a third-party solution like Documents To Go. Also, I wouldn't mind some sorting options -- for the moment, I can't arrange my docs by date, type, or anything like that. My only choices are Owned By Me and Starred.
Even so, I've already found it extremely handy to have such quick and easy access to my Google Docs. Just yesterday I needed a phone number that was lodged in a spreadsheet, and presto, there it was. (I could even dial it with just one tap.) That's some mobile goodness right there.