Some miniSD (not SDHC) cards >2GB do work, as I expected :-).

Here an EMTEC miniSD 4GB 80x (bought in France) was detected properly and does work well (I've filled w/ media files and used them) with my N810 (OS2008: 2.2007.50-2), despite dmesg shows:

.. attempt to access beyond end of device
.. mmcblk1: rw=1, want=3932228, limit=3932160
(not particularly scary)

`df` on the empty card says:
/dev/mmcblk1p1 3985408 32 3985376 0% /media/mmc1

speedtest.sh reports approx 3MB/sec writing and 9MB/sec reading (the internal mmc2 is around 3MB/sec writing and 6MB/sec reading).