At this point I have a fair number of 64, 128 & 256mb sd cards around for my logger project (plus a few 1 & 2gb cards). All are Sandisk labeled, and I tested them with pullups & with pulldown (I used a 20K ohm resistor) just to see what they would do. I have gone through about 50-60 of them with this test.
I have found that some cards draw a low sleep current in my ProMini based logger (usually around 0.33 mA combined vreg & sd card current) even if I leave connections 8&9 floating. However as you suggested, several microSD cards want a pullup OR a pulldown resistor on the two data pins I was not using, without which the sleep currents were much higher than they need to be (some as high as 5 mA) .
But the general result of my trials is: If my logger+Sd card sleeps around 0.3mA with the pins floating, about 50% of the time it increased its sleep current with a pull down resistor, possibly as high as 0.9 mA (the other half of the time the puldown does not increase the sleep current). Most of those cards that started with the lowest sleep current, stay low with a pullUP resistor on lines 8&9, but it does not reduce their sleep current.
If my system draws between 0.5 mA to 2mA with the two pins floating…then a pull down resistor on those two lines will usually brings the whole system down to 0.33 mA sleeping current, while a pullup does not change the sleeping current quite as much (although pullup still reduces it by about 1/3-1/2 as much as a pull down) So preventing the pins from floating is always good to reduce sleep current, but the worse a card is when pins 8&9 are floating, the more likely it is that pulldown will help more than a pullup on those lines.
If I don’t get to near 0.33 mA sleeping with either a pullup or a pull down on the unused lines, then I am calling it a bad microSD card, and wont use it. If my “sleeping system” current for the whole logger is above 2 mA to start with, then I am assuming I have a REALLY bad counterfeit microSD card, and I just throw it in the rubbish bin.
And the WORST cards of all bounce down to a reasonably low sleep current when the system first goes to sleep, and then “creep” upwards over the course of 2-5 minutes, as I am watching the meter, even though the logger is completely asleep. Those cards seem to “creep up”, whether I put a pullup, or a pulldown, on the unused lines. What’s interesting is that they don’t “jump up” like I would expect if they were waking …they just slowly increase the current draw bit by bit. Of course I am watching this with a plain old multimeter, so I am only seeing “the average” go up. Perhaps its a whole bunch of wake/sleep cycles in some kind of self triggering loop?