I'm on a Mac and I use Safari almost exclusively.
Initial thoughts:
1. No more horizontal scroll bar.
2. I can again download the PDFs in Safari.
3. I can launch the compendium from the main page.
4. Near as I can tell, I can launch the compendium from any page.
5. Number 4 seems to be applicable to Dungeon and Dragon as well.
6. When I first went to the website, I didn't need to log on!
7. I'm still logged on!
8. I like the wider layout.
9. I don't like the clutter, but it's growing on me.
Overall, this new website makes me think that WotC is really doing well with DDI and is making a huge effort to better use the internet. 18 moths ago, I pretty much shunned WotC's online offerings, dispute really being into the online community there for a while and making lots of use of their online offerings. Their bringing me back.