English has several variations of this and DL accepts some of them. But I am wondering if Russian has its own variations like English does: Mom and Dad were talking about us. Mom and Dad talked about us Mom and Dad have talked about us. Mom and Dad have been talking about us. Mom and Dad have spoken about us. etc., etc.
As servolock says there is no difference in meaning. But I think he has mixed up обо with об. Об is generally used before a vowel or a vowel-sound. (For example: Он говопил об отпуске)
Обо is used less often. I can only recall some few situations: обо мне, обо всех (about everyone) and обо всем (about everything)
In meaning, there is no difference. I think "обо" is used before words that start with a vowel. "обо" adds a consonant which makes the words easier to pronounce. I don't know all the rules. I know it is also used with "мне". So the phrase would be "... обо мне." Easier to pronounce than "о мне" would be.