I got this card to use with an HP HDX18 Laptop computer that has a built in SDHC reader. I use the 32GB SDHC card to transfer audiobooks to a Western Digital Hi Def Media Player model WDAVN00. I use a USB SDHC reader on the Western Digital Player. Audio playback speed of large .MP3 files is not an issue, but transfer speed of the files from the laptop to the card should be fast.
This is a class six card but it did not have any other speed claims on the packaging. Using the built in reader on the laptop running Vista64, I transferred 30 GBytes to the card in 40 minutes or 12.5 MBytes per second. To ensure that the laptop reader was giving me typical results, I tried the same operation using an external USB2 reader from Connectland. The French made Connectland C1511 reader took 43 minutes or 11.6 MBytes per second. There were 48 large files, all 640MB. The card was factory formatted FAT32.
A smaller, older Lexar SD 2GB card reformatted to FAT32 was able to take 3 of these files, 1.87GB, in just under 6 minutes or 5.4 MBytes per second using the built-in laptop reader.
I got slightly better than a real world doubling of speed with the Verbatim SDHC card versus the Lexar SD card that I normally use with an older Canon PowerShot SD450 camera.
Your mileage may vary.
Based on various SDHC speed charts I've seen, this card is not screaming fast, but perhaps my reader is at its maximum. I won't know until I can get a card that is substantially faster.