Beyond Apple-Google agreement, I have no idea as to how (and if) Maps will be improved in iOS 5. But iOS 5 announcement being just days away, I am hoping it would bridge the gap between iOS 4's Maps and Android Google Maps Navigation app.
I also loved the search feature... You could just type (or speak) whatever you wanted... even just something as simple as "Burger King" and it would take you to the nearest location.
I like Navigon, except it's missing the search like you describe. I wish I could use Google Voice to find the nearest whatever, and then launch Navigon with the address. Not having a google-like search is Navigon's biggest fail, otherwise it's terrific.
The updated apps from Yellow Pages, White/Yellow Pages (Avantar) and Yellowbook now allow voice search via Nuance. Navigon can be launched from either of these after you select the address you want and then select the NAV button.