It is easy to confuse bits and bytes or MBps and Mbps. I have to look it up every time I try to convert from one to the other.
The short version is that the camera creates data being written to the card. At the highest quality setting in an AVCHD camcorder, a Class 4 card is enough. A Class 10 card is three times faster at recording than the camera is at creating data.
Once the video data is on the card, we want to copy (or "download") it to our computers. You can buy the most expensive and fast SD cards produced, but most of us have a bottle neck somewhere. The camcorder plugged in via cord may be no faster than USB 2.0. Our card reader may be USB2.0.
Jogiba is saying that you MAY get an improvement in copy to computer speed if you can find a USB 3.0 card reader and plug it into a USB 3.0 port on your computer, if you have one.
I have a variety of Class 10 cards that are currently prices at about $25 for 32GB. (or is it Gb?). Never has copying to my computer been too slow. In fact, compared to all the other things involved in editing, copy to PC speed is the least of my concerns.
or even a little better:http://www.amazon.com/Transcend-Class-Flash-Memory-TS32GSDHC10E/dp/B003VNKNF0/ref=sr_1_3?s=electronics&ie=UTF8&qid=1364228502&sr=1-3&keywords=32gb+sdhc
Slight waste of money:http://www.amazon.com/gp/product/B007M54E08/ref=s9_simh_gw_p147_d2_i2?ie=UTF8&redirect=true
Gross and extreme waste of money:http://www.amazon.com/SanDisk-Extreme-Class-Memory-SDSDXPA-032G-AFFP/dp/B007NDL56A/ref=sr_1_6?ie=UTF8&qid=1364228417&sr=8-6&keywords=sandisk+sdxc