Note that new posts are converted to the new system automatically. Duplicate sluglinks will get a number appended to them depending on how many of them exist already.
Almost all of the old posts have been converted to the new system as well. There are some that had duplicates and I didn't feel like writing a script to fix them, so for the time being they just link to the old system. They're all pretty old posts though, so no worries.
If things break horribly for whatever reason, you can access posts the old way by changing the "read" in the url to "permalink" -- for example:
This will redirect to the old view.php?post=108305