A few pieces of input:
1. Like others, the logo doesn't stand out. In fact, I didn't see it until I read some of the other comments and adjusted my monitor position a bit.
2. Emphasize the txt'ing capabilities a little more. Assuming you're using something like Twilio, why use that validation code in front of the texts? That makes it highly unusable. You should be able to see what number the text is coming from and attach it to the proper account.
3. Put in an sms reply feature. For example, I text #todo or #grocerylist and it returns my notes that haven't yet been completed with that tag. Which leads to... You've already got the ability to post notes, now retrieve them.
4. The simplicity is totally nice, but how about putting these things into different buckets? Mark as complete, next week, etc... ? That way, you can manage the "boards" on which they go in a level beyond the hash-tag boards. Make sense?
You REALLY should be VERY PLEASED with what you've got here. I'm so impressed with the visual appeal of the app.
My guess is you're using authlogic for authentication. Is that right? If so, there are some good articles out there that will walk you through implementing password resets - in fact, I think it might be in the main authlogic page (been a little while since I've done it). It's really easy to implement.
Looks like I was your 84th user! Congrats and keep it up. I love hearing stories like this.