Take it for what its worth... after all, it comes from me....
I bat a 560-620pa prototypical leadoff batter (high obp, good speed, high sb%) 9th often. As others have said, other than in the 1st inning, the leadoff hitter is not assured of leading off. And remember this... (I cant believe no one has mentioned this).... if you bat him 8th, his SB attempts will be SEVERELY HAMPERED. Most pitchers are at a setting of 5 for SAC. So, rather than risk a CS with less than 2 outs, the pitcher will sac him to 2nd. If unsuccessful, you have a slow footed pitcher on 1st with 1 or 2 outs. If there are 2 outs, he will RARELY attempt a steal, because a CS results in the pitcher leading off. Only players set to 5 in SB att in the settings in my experience, ever attempt SBs with 2 outs from the 8 hole. The negatives of batting 9th are few. One is if the pitcher walks or gets a single (most likely way of getting on base for a pitcher), if he walks or singles, you will likely lose a SB opp, because of the slow footed pitcher ahead of him. Other flaw is if you have a team full of low SLUG%, and higher OBP, the pitcher will come to bat with multiple men on base more frequently batting 8th. Usually there is a drop off at 80 or 100M from 7 to 8 in the lineup due to salary constraints.
Also, in building a lineup, I found that putting all the speedy guys together and all the slower power hitters together helps. If they are intersparced, what will wind up happening is having a ton of LOB. Ideally, you want the speedy slappers together to maximize the single, sb, rbi single opps. Slower players score on HRs no matter where they are on base. Speedy guys can manufacture runs. And if they are consecutive in the lineup, you can maximize their potential. Having 4 slow footed mashers preceded by 4 speedy guys has served me well. I almost always have my lowest BA, OBP homerun hitter hit 8th. I dont want him singling and wasting the hit by having the pitcher strand him.
Just my 2 cents.