Well, it's not quite as good as actually being there (unless you are in the habit of throwing really good parties in your office), but thanks to O'Reilly and (of all people) Microsoft, you can spend a good while learning about what the speakers had to say at OSCON. That's because by now most of the presentations are posted on the conference site, free to download.
Just as with the conference itself, the presentations are a mixed bag. You'll find deep dives into particular technologies ("HDFS Under the Hood"), presentations that focus on a particular market ("Leveraging Mobile Open Source for New Wireless Apps and Services") and more general topics ("Practical Test-Driven Development"). Whatever your open source language of choice, there's likely something here worth your while.
As to file formats, things are similarly confused. If you want to be able to read everything, you need to be able to open PDF, Microsoft PowerPoint, and Open Office ODP files. This shouldn't be a huge hurdle, though it is a bit annoying to see quite so many PowerPoint presentations here.
If you weren't one of the lucky folks who got to the conference in person, you should at least set aside a few minutes to scan the presentation page, and download the ones that are closest to your core work. It's an easy way to keep up with recent developments in the field.