yeah, i get what you're saying. i would think you're probably right about it just being the initial parsing of the query -- that's why i was saying about ORs making the query longer. i imagine both are optimized the same once it starts searching the table, though. the output from explain is the same w/ ORs or IN(), except if you do this
For example, if the query plans are identical (all else held constant) but the initial optimization is faster then you'll see only a .0003s difference as the size of the table increases.
However, if there is something neat with IN then the query times would increase as the size of the rows do..