I'd like the task id field to increment in the same order as the start date, but I have added tasks between existing tasks, so when I sort by start date, the task ids go 1, 8, 15, 2, 4, 5, 7, etc. This is not a big deal but it would just be nice if the task ids were consecutive.
I have found in most cases when the task IDs are listed non-sequentially (the numbers in the left column are out of order) it is because the task list has been sorted. IF this is the case, you can open the Sort By dialog (Project | Sort | Sort By), select (place a check mark in) the Permanently Renumber Tasks option and click the sort button to renumber your tasks.
Note that if your project IDs are out of order because the task list has been sorted, the sort options in the Sort By dialog should correspond to the way your tasks are currently sorted. If for some reason this is not the case, sorting could mess up your carefully crafted task structure. I STRONGLY RECOMMEND backing up (saving) your project before trying to sort or renumber your tasks.
I quote Bob Segrest, PMP Microsoft Project Blackbelt
I had the same question and found the following solution: View -> Sort -> Sort by -> Unique ID
This puts it back into the original order.
In 2010 go to Task Sheet (in View), or change the view while in Gantt view (upper left corner icon) while on task tab. You can use cut and paste, insert, or drag task lines in Task Sheet view . It renumbers the task row along the margin, similar to excel.