I also have no ties to WhitBird or iBird other than being a VERY happy user. I started with iBird Plus in December and upgraded to iBird PRO when it became available. I love both these programs though, for obvious reasons, I don't use Plus as often as I used to, other than to demonstrate the differences to others. Every time I demonstrate this app, others are as blown away as I have been. I know of at least one person who got an iPhone just to get this app.
It is important to have realistic expectations, but from the start I have been blown away by the excellent quality of this program and it's ease of use and how quickly I can find info to show to less experienced birders, without having to fumble through field guides or indexes, and how to use search criteria.
In the very beginning, I did note a few minor errors or imperfections, but the developer really does respond. Very quickly we have seen frequent free upgrades to correct small errors, add new features and add new information.
Please do provide info as to technical or factual suggestions -- Mitchell Waite has been extremely responsive where possible.