From: United States
Not sure where to put this (you should have a "Feature Suggestions" forum), but...
I would love it if with all (many) of your games you had a simple ability to color the notes. You don't need a lot of colors to choose from, just 3 or 4, but...
In any variation of Sudoku, I have different reasons for placing different numbers (constrained by the box, by the row, by the column), and using different colors to represent that will help me avoid the most common mistakes I make (getting confused about why I made certain notes, and either having to completely reconstruct it, or make an assumption and place a number incorrectly).
The same applies to Kakuro.
For Battleship, I occasionally have to try a sort of progression... There are two ways to place the battleship, and if I place the battleship here, then there are 3 spots for the cruisers... if I place one here, then... Colors would help me keep track of my progressions, either by coloring the ship notations by step, or even coloring the water differently (I already tried placing the cruiser there, don't bother doing that again).
This might be an iPad only feature, since there is more room there for a palette, but even on the iPhone, one could imagine swiping left to reveal the palette, or tapping the "notes" button several times to cycle through the colors and actual numbers (and if you haven't placed any notes in one color, then there's no need to show the next color). Or tapping the same number on a square cycles through the colors before erasing it. I'm sure you can come up with some other solutions to this UX problem as well.
Love your puzzles, and I love your "we're not ridiculously greedy" approach to monetizing them, i.e. you don't annoy me into abandoning your games, and I'm more than happy to spend $ every once in a while to be able to keep playing.
Keep up the good work!