I found it hard to use Divine Purpose last season because Ret was squishy and teams like KFC were zergy. Maybe this season DP will be a little better, but keep in mind that it's worth less DPS in PvE than Holy Avenger and Sanctified Wrath, and that it's consumed by dodges and parries.
I still try to use it sometimes 'cause I don't like being tied to cooldowns. /shrug
OP posting on newly 90 pally. I definitely thought Divine Purpose was the PvE talent of choice for DPS. Holy Avenger really accomplishes more in 18 seconds than Divine Purpose does in 2 minutes?
I'd like to hear more people's feedback on DP vs HA.