I recently got myself a new 8Gb micro SD card (for my HTC smartphone). Its actually a micro SD card, but except for the physical size, SD and Micro SD operate identically.
It all worked well, except I had some problems copying data from my older 2Gb SD card.
As soon as I put the 8Gb card in my PC card reader, The PC seemed to freeze for about a minute, and I couldn’t read the cards content.
After some searching around, I found that most older card readers cannot read SD HC (High Capacity) cards.
If you buy an SD or micro-SD card thats 4Gb or bigger, then its probably an SDHC card.
The best solution is: buy a USB multi-card reader that supports SDHC. It only cost me AU$15, so I’m sure most people can get one for under $50.