It would be nice when IE supports the full PNG-24 standard and the full CSS profile. Of course (and this is just a rumor, of course!), there's always a chance that it could ship with Longhorn instead of Longhorn's redesigned-with-the-same-crappy-engine IE 6.05 with this summer's Release Candidate. I'll definitely be buying that, and I'm sure those here with MSDN subscriptions like DJGM will have it even faster than me (since I'll have to wait for the 2-week shipping), and everybody'll get more info then. I briefly used Longhorn, but it was quite unstable (Build 4051), and had IE 6.05. And, of course, I only had a 20GB hard drive, and that got eaten. (I'll have a 100GB drive by the Longhorn RC's).
What I'd really buy into, though, is a standards-compliant web browser that could actually render half the tags I use on HH. Right now, anything using the <abbr> tag doesn't work. Okay, it's a small annoyance, but it's perfectly viewable in everything else. It's where the BIG things come in like CSS3 support. What'd be even better, though, is if they got rid of ActiveX altogether and used an XML-based language to do what ActiveX was doing. Therefore, the user could just block whatever he/she didn't want via JavaScript (in a user interface for those that don't know JavaScript, of course), as so to just block out a tag from running.
I'd also like to see what kind of security features they say they're going to include. If they still use the buggy Trident engine, they're going to run into problems. On the other hand, they could do what Apple did and use KHTML, or they could take existing Win32-capable technology and make a Gecko-based browser. Even if they create a new engine I'll be happy, but it's definite now that 4th-gen Trident is ready to hit the junk heap. If they do use Trident, they're DEFINITELY going to need help patching all those holes before the RTM.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.7) Gecko/20050414 Donzilla/0.7PR1 (like Mozilla/1.7.7; wml/1.3)
Laptop: HP Compaq nx6325 - Turion 64 X2 @ 2GHz, 2GB DDR2, 100GB HD, ATI Radeon X300, 15" LCD, Seven Pro
Handheld: Palm Treo 650 - Intel PXA270 @ 312MHz, 10MB RAM, 32MB flash, 2.7" LCD, Palm OS 5.4