What else is sluggish apart from video?
If it's just video I might be inclined to try and update/reinstall the graphics drivers, though I'm not sure how to on OS X...

Activity Monitor, in Utilities folder, can tell you what is hogging performance. It lists all processes running and what %age of cpu they use.

Well, it seems to be mostly video IIRC.

It struggles even with HD movie files.

Flash games (even simple ones) bring it to a stand still almost.

When playing iPlayer in HD it slows down so much that it takes up to 10 seconds for it to recognise the button press just to close the Safari window it's playing in.

I've got an iStat widget to monitor CPU etc... but there never seems to be any CPU or GPU activity that would suggest anything is hogging performance.

I'll take a look at activity monitor tonight to see if I can see anything there.

That would lead me to look into the graphics card/driver.
I'll have a poke around

I did a bit of googling last night but the only thing I could find was to use Software Update to update the graphics drivers.

If you find anything else let me know and I'll have a looky

People over at the Apple Discussions seem to think Software Update is the best way to go...

A couple more questions that spring to mind, are you using your Mac for f@h? I found that even my Mac Pro became sluggish after running it for a while. My thinking here is that IIRC f@h can use the GPU for processing, if you have that turned on you wouldn't see it so much in Activity Monitor.

Does anything look untoward in your Console? Are there lots of errors/messages being printed when you are doing graphic intensive things?

Lastly, have you tried re-applying the latest combo update? http://support.apple.com/kb/DL1361

Sorry it's not a definitive answer...

Ben

No need to apologise Any help is a good thing

I don't do any f@h so that's not going to be it.

I'll take a look at the combo update thinger. As for software updates I'm fully up to date at the moment. I'll have a look at re-applying some updates I think.

Also the KB pointed me in the direction of the energy saver prefs. Worth taking a look maybe.

On some Macs (certainly under Tiger and Leopard) you can/could choose optimum battery life or optimum performance, perhaps yours has that option? My old MacBook doesn't, which suggests to me it may have been moved/removed from Snow Leopard...

Yeah, mine doesn't have the performance option stuff.

I did just realise that I was using the Leopard version of Onyx. Just downloaded the Snow Leopard version and running through that again.

If this doesn't work then I suppose it's probably a hardware issue that ain't gonna get any better. My next option would be a replacement and that isn't going to happen any time soon.

I presume you are no longer covered by Apple Care, but if you could take it into an Apple Store then I wonder if they could suggest anything? Even if it's just extra tests to find out what the cause is...

Yeah, take it into an Apple Store for a diagnosis. I took my old MDD in for a check (I think it was just RAM) and they offered me a free check.
They can only say no!

Have you tried this yet, Foggy?

A quick Google suggests other products are also available. Try monitoring the temperature while playing a video, and see if it goes above about 70C and if the fans are maxed out:

This widget looks nice: http://www.islayer.com/apps/istatpro/

Worth checking to see if any if the vents are blocked. It may be worth taking the back off and seeing if there are blockages caused by dust, fluff etc.. A can of compressed air will help shift that out.

Ooh I'd forgotten about that, and I've got it installed.

They also do a menu bar version. Very handy if you want to monitor network traffic.