Howdy Fintan,
As Martin says it's really quite important that you are consistent in using the same arrows to centre (most of the ASGT group say Up and Right). Otherwise the inherent backlash in the gears will mess things up a bit (not by a huge amount though). It does make a difference.
Also, the first few times I used Goto the performance wasn't great but what I didn't realise at the time is that the mount will train itself to deal with the cone error of your mount/scope combination (i.e. the small difference in angle between your scope and where the mount is pointing). So after the first few sessions goto performance improved quite a bit.
I found the default settings for backlash fine for visual use but had to adjust it to get autoguiding working satisfactorily. If you're not imaging I wouldn't bother as it is very time consuming (it was for me anyway).
By the way, there is a wealth of information on this mount available on the celestron asgt Yahoo group & a bunch of people always willing to help.
groups.yahoo.com/group/Celestron_AS/
If you are sufficiently aligned and the object is still drifting you could have the same problem as I have had on my own asgt since I got it. If I use the left arrow at all, the scope will continue creeping in that direction at it's slowest setting (.5x sidreal) until the right arrow is pressed enough to clear any backlash.
I'd also check out the DEC marker on the scope, mine was off by about 10 degrees when I purchased mine so I had to remark it and use the new marker.
Cheers,
Trev
  