I wanted to add USB 3.0 to my Thinkpad T420 so I decided to pick up a cheap 34mm NEC controller based expresscard USB3.0 adapter on Amazon.
The NEC based USB controllers have been supported by the Linux kernel since version 2.6.31. However, in Ubuntu 12.04, it isn't quite a plug and play affair. I had to run the following command to get my laptop to recognize the PCI expresscard.
sudo modprobe acpiphp
Once you do that, you can check to see if the system sees the device by typing in:
lspci | grep USB
Once you see the NEC USB 3.0 controller, you are pretty much good to go. You will need to do this after every reboot unless you modify your GRUB boot loader. Also, I had to disconnect and re-connect a few times before my laptop could see the card.
Next, there is the issue of power. Some portable USB 3.0 devices need power and the particular adapter I have uses a USB pass through cable to connect to a free USB port. Unfortunately, this was a trial-an-error. Certain ports of my laptop did not generate enough power for a 2.5" HDD drive. The only one that worked for me was the lower esata/usb combo port. Furthermore, there is one thing that these expresscard manufacture fails to mention is that you only have enough juice to power one USB 3.0 device. USB 2.0 will only have about 5 volts worth of power so it make sense that only one port will be powered.
Now for some speed benchmarks. The expresscard USB adapter did make a difference.
As you can see below, with a Seagate Go Flex, I got almost twice the read speed using USB 3.0
USB 3.0 w/ 1TB Seagate Go Flex HDD 5400 rpm portable drive. The results are acceptable considering the source is a platter hard drive.
USB 2.0 w/ 1TB Seagate Go Flex HDD 5400 rpm portable drive. As you can see, USB 2.0 is very slow.
I also wanted to test it with an SSD and I got some decent results.
USB 3.0 w/ 128GB Crucial M4 SSD. These results are almost as a good as plugging a drive to the eSATA port.
I did not test the card in Windows so I can't comment on the Windows performance. However, if you are an Thinkpad Linux user, I strongly suggest getting an expresscard USB 3.0 adapter for your older rig. It is well worth the investment.