One my database has from 400 to 1500 connections in same time.
DB works im mixed mode:
-- all DBA use dedicated server connections
-- all "usual" users works thru application server and use MTS connections.

Oracle version : 8.1.7, OS solaris 8
SEMMSL = 4096
avg semaphores utilization around 60~70 %
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I can estimate max # of connections in this DB as 1000/0.6 ~= 1650
where 1000 -> avg # of connections, 0.6 semaphores utilization
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