A lot of you apparently don't appreciate the way that TIPs work and are not giving them sufficient credit.
At present, the "current yield" on long-term TIPs is about 2.4%. That means that the annual interest payments amount to 2.4% of the current market price of the bonds. The current market price is closely related to the par value, and the important thing to understand is that the par value gets "bumped up" at the end of each year in proportion to the actual inflation that occurred.
This "bump up" represents a return that is in addition to the interest payment for the year. (For tax purposes, it is reported separately but also subject to being taxed as ordinary income on the federal return but not on the state return.) Thus, if inflation for this year turns out to be, say, 1.6%, the total (annualized) return on long-term TIPs purchased now would be 2.4% + 1.6% = 4.0%.
If you go to FIRECalc, you find that a portfolio of 100%TIPs yielding 2.4% (with no expense charge) would have sustained a 4% withdrawal, inflation-adjusted, for 30 years in 100% of the trials.
While I think that most early retirees can do better than a 4% withdrawal by having some stocks, high yield bonds, etc., it is hard to beat the safety of TIPs, and the return that they will sustain is not all that bad. For an older retiree who wants complete safety, it would make sense to have 100% of their assets (other than some cash for immediate spending) in TIPs.