Yeah, I have kinda noticed that also. My first thought when I noticed it was that the phone is indexing the content. Which probably it was at first, but even after a few days it still was slowing down in use. I used my N79 for testing, and had the latest firmware on the device. Taking photos and recording video was my major test, also I had all my messaging on the memory cards - SMS and email, and contacts (800 or so).

I THINK that fragmentation and wear are the two major issues with transfer rates slowing down - but the phone seemed a little slower to use and that would have nothing to do with (constant) reading/writing of the card? Random seek times probably affect the writing times as well, and even my 8GB and 16GB cards were the same brand and speed class, I know that the writing speed isn't compared/spec'd with the class ranking. Also, wear leveling might be something that wasn't perfect with the N79?

Obviously I'm not well educated in (solid state) memory tech, but ultimately I just concluded that having more space slowed my N79 down and the reason remained unknown.

So... I'd really like to see some tests done with the N900 and different memory cards - at the moment I can't but I really need to do some tests myself too.

And the way the N900 uses memory is radically different than in the N79, in practical use N900 accesses the SD card much less as the internal memory is used for most of the before mentioned read/write tasks, camera is the only task accessing the external card so that fast access times probably don't matter with the N900 as much? I'll be taking a lot of video and I have the internal memory full of mp3's so a bigger-than-8GB card is on the shopping list.

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I personally never had any doubts that the N900 wouldn't support large MicroSDHC cards, It's not like it's debatable as the SDHC standard has that size specified.