For those of you with your spouse owning the only Roth IRA, note that if you inherit it directly (not through the estate), you are treated as if you owned it all along. That means that as long as your spouse held the Roth at least 5 years, all your distributions are fully qualified and tax free. You would simply roll it over to your own Roth IRA. If not held for 5 years, the holding period continues to run until you reach the 5 years in total for both spouse's holding periods.
The only issues occur if there is a divorce and one spouse is left without a Roth as part of the settlement. If the spouse without a Roth is awarded part of the other spouse's Roth in a "transfer incident to divorce", the receiving spouse who has not had a prior Roth of their own would probably have to start a new 5 year holding period, since there are no IRS Regs that establish that the transferee is to be credited with the prior holding period of the transferor.