As most you already know, Notification Services is not part of Microsoft SQL Server 2008. I think this is a shame since SSNS is really a great product. It may be rather complex at first glance, but it's a great product nonetheless. I'll probably devote a blog to it's abrupt deprecation at some point in the future.
In the meantime, if you're preparing to upgrade to SQL Server 2008, you should verify that you don't have any rogue SSNS instances running on any of your servers. I hope your environment is more controlled than that, but I've seen more than one shop where change control was, well in a word, uncontrolled.
So, how can you tell if a server has a SSNS installed on it? Run the following query in the msdb database. It'll list all SSNS instances installed on that SQL Server instance.