First off, the landscape notes view in Evernote 3.0 is stunning, you can scroll through icon sized images of all your notes with a few flicks of the screen.
The first thing you will notice when you open Evernote 3.0 the first time is that all of your notes load in a "All Notes" modes, no more loading and scrolling through 25 notes at a time. In portrait view there is an "Index Bar" floating on the right side of the screen (the index bar is along the bottom of the screen in landscape view), the index bar can be configured on the fly to group notes by: created or updated date, title (alphabetically), city or country (assuming your notes are geo-tagged), or by notebook. I have 300+ media rich notes and resorting by the grouping took less than 2 seconds - very impressive. To select the grouping press the "i" icon to the right of the search field. I found the notes grouping to be a good default view for the iPhone - mimicking the desktop view.
Search and advanced search have had their interfaces cleaned up and advanced search now offers an "Other" category that lets you filter by source, such as "Emailed to Evernote" or mobile, etc.
All is not perfect with this upgrade though, you still can not edit notes on the iPhone that contain "stylized text" or images - hopefully Evernote will find a solution for this with the new tools provided in iPhone os 3.0. Also, the voice note functionality has been reworked, the new interface is nice - fewer clicks to begin recording, but the sound quality of the recordings is poor. To compare, I used Apple's new Voice Memo application and emailed the recording to Evernote, the sound quality was superior to the recording from within Evernote - noticeably superior.. so much so, that I plan to use Voice Memo and email the audio file to Evernote, until the quality issue is addressed within the Evernote application.
For your notes that are geo-tagged, such as notes created on your iPhone 3G, you can now view your notes on a map. This feature is acccessible by pressing the push pin left of the search field. I am not sure how useful this will be for me, time will tell.
All in all, Evernote 3.0 is a great upgrade - highly recommended, I look forward to using Evernote 3.0 on the 3G S - the increase in speed should improve productivity, not to mention the improved autofocusing camera!
If you are already an Evernote user, there is no reason to skip this upgrade, if you have not used Evernote, now is the time to jump in! Evernote on the iPhone is like carrying a room full of filing cabinets in your pocket! In a word.. AWESOME!