Hi there,
You can still do quick searches in just the same way you could before. The only difference is that now you use the combined address/search bar rather an the google search field. I also believe (someone feel free to correct me) that you can set your default search engine in he Safari preferences this means that when you type your search you will get the results from your chosen search provider.
I have to say though that google is pretty much the daddy of search engines so having that as an automatic default makes sense.
Once you have retained your muscle memory and have getting used to looking for the address bar and not the search bar you will find that this new feature is much more powerful than it was when they were separate.
The thing that I don't understand is why they have not release dan update for mobile safari in order to unify the two fields like the have in desktop safari. The way it is at present, iCloud can not sync your searches with your safari any more because they have two separate layouts. Before when I went to use my desktop safari and started searching in the google bar, all the searches that I made on my iPhone, iPad and iPod also came up (and visa-versa), now, because of the different layouts iCloud is not able to sync my searches, which has left me to rely on the my history (which I loud still syncs). Maybe we will see a fix for this in iSO6, but it would have been nice if they had released an update to iSO5 that brought the two different versions of safari in tune with each other.