the biggest ARCHITECTURAL difference is that 8i has native Java support (JSQL, server side JVM, etc.). other than that dbwr (et al) is still dbwr (et al), SGA is still SGA (although there's a "Java pool" which can be a real hog if you're using lots of Java), etc.
from a PRACTICAL standpoint the biggest differences I've noticed are:
1) the new Oracle Universal Installer (OUI) REQUIRES an X-windows server (i.e. it can NOT be run from a character only terminal). If you run Linux on your workstation (or have an X emmulator for NT) you can export DISPLAY back to it and still run it remotely but it's REAL SLOW (at least compared to 8.0.x character over telnet or even ssh1). on the plus side A) the new inventory manager is 100x better than the old asset manager and B) I've yet to have OUI crash on NT and screw up the resigtry (at least for clients) like 8.0.x installer did (remember 8.0.x. installer & Y2K? ;-)
2) TNS configuration is (optionally) different/"enhanced" for internet but no need to elaborate here.
other than that it looks almost identical to me (at least from a DBA's standpoint).
just my 2c/never 2bHO!