Bookmarks are imported but if you've spent loads of time tweaking firefox it's possible you won't like it. You could always run it side by side though. Personally I have firefox 3, internet explorer 8 and google chrome running... I'm now thinking of trying opera too for a good comparison.
It comes with a spellchecker built in and is pretty much configured corretly from the word go... though I'm not sure about profanity filters.
Ref Incognito mode not logging browsing history... personally I think that the marvellous thing about having IE8 at work... they can never tell where I've been because it nukes the history and everything as soon as I close it.
*sigh* i downloaded it the day it came out, and used it for about a week (i still have it, have just decided to stay with FF3 until the full release of google chrome is announced.) i love google chrome, it is by far the fastest web browser out there. also, another one of my main concerns is the amount of tweaking and customisation you get with FF3. remember people, all that will be possible with the full version of google chrome, once it comes out of beta testing.
customisation will be as good as, if not better in google chrome than in firefox for a few reasons (it should be a very similar process for the two, as they are both 'open-source' programs) the main reason it will be better in chrome is simple, its GOOGLE! its faster! its simpler! it has more options for methods of easily customising (script made easy)
at the moment, we are only seeing the very backbone of what google chrome will be, and what it will be capable of. they have given us the best of the best, to catch our attention, now they will slowly release the many AMAZING features they have up their sleeve to once again, corner another market. GOOGLE FTW!