**EDIT** more on this Here
I did a search and couldn't find anything here (too easily anyway!), so just thought I'd give a heads-up to you fine people about fake CF cards on ebay. (Mods - if there is anything then feel free to merge or whatever)
The bad news is - I got one!
The good news is - the idiot shipped it without charging me!
So I have a free and very fake Sandisk Ultra II 2gb CF card. I timed transfers compared to a genuine Ultra II, a Lexar 80x and a bog-standard Sandisk 256kb.
The method used was fairly crude, but certainly did the trick. Set the 30D to high-continuous, start stopwatch at the same time as finger hard down on shutter, hold shutter 'til buffer full (12 shots) & time until red light goes out.
The results were (roughly) as follows:
Genuine Ultra II: around 14 secs
Lexar 80x: around 14 secs
Sandisk 256: around 25 secs
'Fake' Ultra II: around 25 secs!
The card looks genuine (hologram effect silver logo on sticker), but I suspect it's a (maybe even Sandisk) standard 2Gb card. I got mine 'OEM packaged' i.e. no packaging, but I have heard of convincing fake packaging complete with hologram foil seals etc.
So I guess - buyer beware. I hadn't heard of this 'til after I got one!
Update:
I received a 4Gb Extreme IV as a gift from a family member last Xmas (complete with fancy box, pouch, mini-CD with recovery s/ware), and hadn't really used it yet. I just enquired as to it's origin and 'ebay' was the answer, and the seller is mentioned in the other thread linked above, and also here
. Hmm - not good I thought.
I ran a comparison using HDtach with my UDMA-4 Reader and a genuine Extreme III that I already owned. The III got 19.8MB/s burst, 19.4MB/s average, 0.7ms random access - which is comparable with the spec'd '133x' (20MB/s) for the Extreme III.
Incidentally this is over 3MB/s faster than Rob Galbraith's tests could achieve with this card using any card reader on any system in his useful tables (which does make me wonder about the validity of his results a little! 
)
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The "IV", however, scored 16.1 / 15 / 1.1ms for the same tests with higher CPU usage - a long way off the spec'd '266x' (40MB's) that a real IV is capable of, and is most probably a rebadged (Transcend?) 100x card.
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So I'm now the not-so-proud owner of 6GB of fake Sandisk storage! I have used the fake Ultra II numerous occasions (last resort usually) and I haven't had any problems with it, although it is slow to clear the buffer and slow to clear down to the laptop - but no failures as of yet 2 years down the line (touch wood!).
