Problem
If you complete the druid quest, but don't talk to Guth'Alak before reaching level 30, the rewards are permanently forfeit.

How to reproduce it
Accept and complete the Kill Keethrax quest. Don't talk to Guth'Alak ever again until you're level 30, then do so, and he'll tell you about the greater white unicorn who seeks your help. The rewards from the previous quest are now lost forever.

Notes
This is extremely unlikely to happen in a regular game, so maybe the druid could comment on that. "Well, that took ye pretty long! Anyway, here's your stuff. Now, there's this glade in the forest..." :)