Depends a bit on how long a period you like to look at. You can use the sys.dm_db_index_operational_stats function and look at the leaf_insert_count column. But since it's a DMV it's cummulative and it will be cleared when the SQL server gets restart.
You could setup a job to collect the the values daily into a table, and then calculate the deltas.
[font="Verdana"]Markus Bohse[/font]