Today, the mortgage bond market was off by as much as 51 basis points. This in turn, caused mortgage rates to go up. Since investors aren't paying much for purchasing closed loans these days, the spread between rates is much lower than it has been over the last 5-7 years. So a large decrease in movement like we saw today could change interest rates roughly .375% in rate. So today probably wasn't the best day to lock in a rate.
On another note, did you know that when applying for an FHA loan, both spouses have to have their credit run even if one of them isn't going to be on the loan? The purpose of this is to add the non-applying spouse's monthly debts against the actual applying spouse's debts since they are married and will be living there together. So if your spouse has lots of debt and you are thinking that by applying as a married man/woman as your sole and separate property, you could avoid the other persons debt, that will not be the case on an FHA loan.