I am not sure if it was more of tradition - many older people will tell you that is a good day to plant - or if it has more to do with my dad always had that day off from work. No matter the reason - we always had a great garden. There are great memories from that time.
The local UT Extension office, I know since I am there all the time, recommends planting after April 15th. So, I guess we should be safe past any killing frost.
Now to just wait and hope to enjoy some fresh onions, squash, cucumbers, tomatoes and corn.