Scorpions make a great early seafaring mount if you hold the jump key ( space bar by default) a scorpion will float above the water allowing you to get past most Puranas without being attacked, this can be extremely useful for crossing dangerous rivers or even oceans.
Very effective as a battle mount/travelling companion. I mostly play on single player so an effective companion is vital. I tamed my Kopiona when she was level 32...she's at 62 now with 200% melee damage, over 800 health and quite a few surprising kills notched into her tail.
Some noteworthy accomplishments (without my assistance) are:
-1 Carno killed (lvl 30)
-1 Spino (lvls 3)
-1 pack of 4 Raptors (lvls 36, 24, 18, and 50)
-Survived a Rex attack (lvl 24) after I had died with minimal health loss.
Coupled with its torpor inducing attacks, it's also great as a taming mount.