Smartypig seems to be legit with full FDIC coverage. The 2.15% is only good for the first $50k, but it's 2% more than I'm getting anywhere else, so about a month ago I started depositing money there.
There are limitations. You create "goals" and you cannot remove money from a goal without closing the goal. So while it's fairly liquid, it's not as liquid as a straight savings account.
However, there isn't anything preventing you from creating 10 $5,000 goals rather than a single $50,000 one. So if you need to temporarily withdraw some money, you just close out one of the goals and when you're ready to put it back, just create another one.
It's only as "public" as you want it to be. One of the features is that you can create a goal that friends and relatives can contribute to. However, you don't have to share the goal with anyone else.
Another limitation is that you cannot have a joint account. However, there is a survivorship option that will allow your spouse to retrieve the money in the event of your death. You can also make sure your spouse has the password so they can remove the money if they need to.