"(2005 Quad G5 Tower w/OS X 10.5.5, multiple Seagate ST31500341AS firmware SD17 drives (internal and external))
Update: I am now facing some problems with iTunes - importing files takes ages - I've already contacted Seagate Europe and they were not aware of any problem.
So I am too facing severe performance issues. (check the console app - I'm guessing there's journaling related messages there as mentioned in a report from a Mac Pro owner with this drive.-Mike)
Importing of 40 video files into iTunes (approx 4GB) took some 2 hours!!
(I asked if he's now seen the issue on his internal and external drives as he mentioned using both in previous report.-Mike)
let me try to summarize my findings of today - but first my setup:

1.) Two 1.5 TB Seagate drives in my Quad G5 connected as Raid 0 over the built in SATA 150 connections in the factory bays

2.) Two 1.5 TB Seagate drives in a Taurus FW800 casing with setting for two individual drives + connection via software in drive utility from OS X. (connection via software?)

All 4 drives have Firmware SD17 (the only version shipped to date as far as I know.)

The performance issues I saw happened with the internal drives in the Quad G5. The external drives are connected via FW 800 + the built in FW 800 connector in the Quad G5.

(I asked if he tried turning off journaling (tip/how-to in yesterday's news).-Mike )
I switched off the journaling and the performance went significantly up to a level I was sensing with the Hitachi 1 TB drives I used before. (maybe a bit better - had no time to evaluate in depth the speed - just a guessing)

No drop outs on Video or Music so far (was testing a SD video for 30 minutes)

Question: What happens if my Quad G5 crashes? Is journaling enhancing the security of the data integrity? (See this apple page w/notes on File system journaling, although for years we ran drives w/o that. Regardless, always have a current backup of important drives/data. And I would personally not run these drives in RAID 0 (in fact I'd choose another drive period based on what owner's of them have reported so far).
The fact journaling enabled causes periodic I/O stoppages IMHO is a clear sign there's some more basic compatibility issue present - and disabling it may help (owners say) but that doesn't mean it's a total fix (or that it's the only problem you will see).-Mike)

The Mac feels now more snappy and "normal" again.

I wrote an email to Seagate Europe with the problems and had a phone-call with them. They were not aware of any problem but they promised me to look after the topic.
-Joachim
(my drobo is a real help and safety line here ;-)"

FYI - Joachim later wrote (Nov 1st) that his RAID-0 (stripe) set crashed. His last mail also included a reply from Seagate support that basically said they're still trying to replicate these problems, which seems odd considering how many owners have.
BTW - although I doubt that's the problem (since even 2008 Mac Pro owners with 3Gb/sec SATA saw this same issue) I wrote to ask if he'd try forcing SATA 1.5Gb/sec mode via jumper. (I downloaded the general seagate 7200.11 manual and it does show a SATA 1.5Gb/sec jumper option.) I also checked for any info on SSC (spread spectrum clocking) enabled on these, but no mention of that for these that I can find. (SSC was an issue with some early drives years ago including the first 7200.9 shipments, but I don't think it's enabled anymore on most models.)

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