I have re-initialize some subscription. After generated snapshot
successfully, the synchronization view showing 'The process is running and is
waiting for a response from the server.' and I found the replication process
is under 'async_network_io wait'. The job has run for more than 8 hrs. Any

I'd check on the subscriber that something is actually happening - you could
use profiler or dbcc inputbuffer (or dm_exec_sql_text for SQL Server 2005)
to see that the merge agent is actually doing some processing. If nothing is
happening, then I'd investigate network connectivity and bandwidth issues.
Cheers,
Paul Ibison SQL Server MVP, www.replicationanswers.com
(recommended sql server 2000 replication book:
http://www.nwsu.com/0974973602p.html)