Though I use Chrome almost all the time, I like IE9b and when it is released finally, I would like to use it full time because I think it works well with the Office apps. But what I'd like to see improved in IE9 (the final version) is:
(1) The realignment of the tabs (which as Darician says above will be fixed). This is really good news!
(2) A better/ more efficient Password Manager and how automated forms (including username and password fields are filled in - I like how Opera executes this and to a lesser extent how Chrome handles this. No idea about FF since I don't use it).
(3) There is a desperate need for an effective pop-up blocker. The inbuilt one is not very good and when set at the highest levels, it interferes with how links on pages open (either in color tabs or in new windows). Here is an example of a page which is very irritating in IE9b but which runs well (without popups) in Chrome:
The Times of India: Latest News India, World & Business News, Cricket & Sports, Bollywood
(4) This one is a wish actually: I wish there is an app that allows me to send webpages directly to Windows Live Mail to be sent as an email. At the moment righ-clicking on a page allows you to send by Gmail/Live Mail etc. provided the relevant add-ons are installed. A similar add-on to send to the WLM email client would be nice and very convenient.
(5) Lastly, I notice that there is a bit of a lag when IE9 starts up as compared to Chrome. There is also a lag on opening webpages (again compared to Chrome). I don't why this happens, but I have tested this on quite a few machines with varying connectivity speeds.
If IE could handle most or all of these points, I think I would immediately move to IE9 and use Chrome as a secondary/backup browser.
Thanks
Edit:
(6) Someone mentioned spell check. This would be cool as a built-in feature of IE9 (the final release).
I should also add that what I do like a lot about IE9b is that text on sites (generally) are rendered very well - even compared to Chrome.