I try not to as I like my conversations however, I have heard of issues of going past say 1000 messages; I believe from my own experiences that this performance issue is related to the sqllite database being used. As it is, I use a terminal to copy my db files that contain the messages off to my sdcard just to cover if an issue occurs. Can always copy back to view the messages.
Sent from my R2D2 using DroidForums App
Even when you 'delete' a text message inside the text messaging app the message is not deleted. Auto delete doesn't work either.
Go to Contacts then scroll to the left and you'll see they're all still there. On that screen (Contacts History) select Menu and then Clear History to get rid of them.