I am doing something very similar as yourself. Moving from 9i (18.104.22.168) (Solaris 9) to 11g (22.214.171.124) (SUSE Linux 11).
The DB his 24/7 system ! On SUN servers where warranty will expiry in June.
There are 2 parts to this:
9i (126.96.36.199.0) - patchset 188.8.131.52.0 (direct) + 9373986 (patch)(DB capture) - same server. This allows direct upgrade to 10g. (10.2.0.4.0) using dbua.
(10g-dbua wizard has bug - create full rman backup yourself plus do not move files, as part of dbua) (quick)
10g (10.2.0.4.0) to 11g (184.108.40.206) - use TTS (http://msutic.blogspot.co.uk/2009/11/cross-platform-migration-large-oracle.html)
DB replay + SQL Performance Analyzer. -part of Real Application Testing.
9i to 11gr2 has plenty of pitfalls - e.g. running of queries.
Upgrade itself his tricky but, this will not guarantee the success
Very good paper 'Upgrading from Oracle 9i to Oracle Database 11g: A real World Customer Experience'
The client has Dataguard Standby 9i Database also.
I need to test Dataguard on initial patchset + patch to 220.127.116.11.
what version of 8 are you using plus what OS ?
what destination of 11g plus os ?