markvran:

Russ - Thanks for the information about HSBC. Online saving accounts are new to me. I just visited their website and am amazed. Twice the rate of the prime money market and its backed by FDIC! What's the catch? Are these widely used by Bogleheads? What, if any, is the downside?

There is a maximum deposit amount backed by the FDIC.  Depending on how much the "significant amount of cash" that you mentioned in the starting post of this topic is, the FDIC may not back all of it.

In general, the maximum at each bank is $100,000 per depositor, an additional $100,000 for the depositor's portion of joint accounts, and an additional $100,000 for each qualifying beneficiary of a revocable trust account owned by the depositor.  A qualifying beneficiary is a spouse, child, grandchild, parent, or sibling.