FileMaker developer, Jack Rodgers, just bought one of the new iMacs and tested out a few things running FileMaker 8 Advanced as a client to a FileMaker 8 server. With 2 minutes of testing, it seemed to work fine.
Filemaker 8 Advanced during a short 2 minute test against my FSA copy of Filemaker 8 Server ran flawlessly. Some things were noticeably faster than they were on my 1.33 Ghz Powerbook while one or two things such as a go to record script setting values in a portal of maybe 50 records. However this was a fresh startup so there may not have been much data in the cache. My guess is that it will run OK for developer purposes at home or offsite but no comment on how it will run on a client's network. ...To sum it up, it would appear that the shipping iMacs are working OK but insufficient work time to declare them trouble free with Filemaker 8. - Jack Rodgers
That doesn't mean everything is fine running FileMaker under Rosetta, but at least it might indicate that FileMaker Inc. is still testing FileMaker 8 prior to OKing it for Rosetta. They may just be conservative and want to make sure that absolutely everything works before signing off on it.
Or, there may be serious problems. But, at least there's hope. Sounds like the performance is decent also.