I check quarterly or when I have a larger-ish ($1000k+) lump sum to invest. That's so that I can update my freakishly detailed spreadsheet and use the investment to help balance my portfolio and steer it back toward where I want it to be.
Other than that, I simply don't care what they are worth. Husband and I are at least 12 years from "retirement" (and he will almost certainly want to work far longer than that, in some capacity), so the balances just don't matter, and I am not in anything risky enough that I am going to mess with it based on performance.