On the Omnia i910 this app seems to work well. Taking into account the beta status and your list of already knows issues + goals, what you have so far seems to work as advertized, doesn't have resolution issues, and seems moderately stable (I have crashed a couple times, but I can't pin it to the app alone (can't reproduce exactly)).
It may just be me, or maybe when the menu screen is tweaked it will be clearer, but for an app that is primarily based on figuring tips + bill splits, I would think it would be easier to open on the 'bill screen' first, and allow you to navigate to the calculator from there. (I can't remember what screen it started with because in looking again I may have uncovered a bug, I am stuck on the 'even/split' screen whenever I open the app.)
I also noticed you can'r enter more than $100 and change on the bill screen, and I know it may look cooler to have a scrolling choice area like it has, but maybe each digit could be altered allowing you to chose the hundreds place, the tens and the ones individually...either by scrolling menu like you have, a rolling one like another 'fruity' phone
or have a numeric keypad pop-up. I know you can enter it into the calculator, but it just seems to me that by the time you get to the splitting stage you usually have the bill already and don't need to add it together to figute the tip or split.
Just my opinion, I may be in the minority, but overall....so far it is looking pretty good JCerna!!