Depends on the volatility of your profession. I currently feel very secure in my employment. Combined with the fact that I don't make a ton of money as a young professional, I only have about two months living expenses "cash" as I'd prefer to at least attempt to max out my Roth, and I'm not making enough to do both and enjoy the things I enjoy doing. Even if I made significantly more, I don't think I would go much above three months cash, as it is far too easy to put sudden expenses on a credit card to give myself time to pull contributions out of my Roth penalty free or liquidate some individual equity holdings, as another poster has suggested.
Getting sub-1% on a big chunk of change strikes me as unwise when there are so many other options. Put another way, I would be more concerned with how much capital you can have access to within, say, 15 days than what you can have access to in 15 minutes. But, that's just my opinion.
This post was edited on 7/27 at 12:11 pm