I keep confusing your choice tag symbol (&) with the # symbol which you chose to use as a symbol for project.

The reason is that I am used from Twitter to using # to tag posts with hashtag. I'm sure that most Twitter users find it confusing. As Twitter is a very popular platform, it's a mistake to confuse users. It's like you would come out with your own keyboard shortcuts for doing cut&paste, instead of CTRL+X and CTRL-V. You don't want to drive new trial users away, do you?

As a Mac user who is using typing in Hebrew, it's also annoying for me to type &, as when the keyboard is in the Hebrew mode, shift+7 generates the local currency sign (Israeli shekel). I have to switch to English in order to type shift+7 and get the &. The same is likely true for other languages.

I know you may not like changing terminology after the product is out, but this is really early in the game for Doit, and most of its user base is still to come. Choosing & instead of # to denote tags is a mistake - and it's best to fix product mistakes early on when they have caused the least damage.