1) I always enjoy a lively debate.
2) I still don't think it defeats the purpose of the puzzles or of solving them 'on your own', per say. In it's simplest form, it is a tool, which aids in the solving of the puzzles. It does not simply solve them for you (while that is an option). And this is not some sort of 'weak' excuse.
3) There are levels of difficulty inherent to most any logic puzzle of this sort: the less information revealed, the harder the puzzle can be to solve. It is nonetheless solvable, but may require more leaps of the imagination or the use of brute force logic. So, if you can do it all in your head, I commend you. I, personally can't. Yet, I have always loved logic puzzles and Sudoku, by far, fits the bill. And, to me, being able to work out the puzzle on a computer, in the same manner I would on a piece of paper, is a very nice alternative. Now, that' s just me & maybe I spend too much time with my iBook, but simply because I solve the thing on a computer vs. a piece of paper hardly amounts to defeating the purpose of solving the puzzle via my own mind via the use of logic. I'm still doing all the work, trust me. I'm not one to cheat and would much rather leave a puzzle unfinished, then 'forcefully' solved.
4) Yes, I am relatively new to Sudoku and, possibly, as I continue to solve them I will find such software as this pointless or come to agree that it is a means by which I am 'defeating the purpose' of the puzzle. But, until then, I will support it.