I have been running Oracle + Reiser for a long time. I don't see any performance problem, in fact it may be quicker and it sure is a lot more reliable.
Another benefit is not waiting 30 minutes for fsck when you reboot (i.e. kernel changes).
Linux up to 2.4.5 (I believe) were screwy any way and kernel 2.4.9 had some VM performance problems. Use 2.4.12 and all should be well.