New: System is unresponsive while using dd to copy DVD ISO to USB stick/key

https://bugzilla.kernel.org/show_bug.cgi?id=34132

Summary: System is unresponsive while using dd to copy DVD ISO
to USB stick/key
Product: IO/Storage
Version: 2.5
Kernel Version: 2.6.38.2
Platform: All
OS/Version: Linux
Tree: Mainline
Status: NEW
Severity: high
Priority: P1
Component: Other
AssignedTo: [email protected]
ReportedBy: [email protected]
Regression: No

When I use

dd if=<some_iso_file> of=<device_of_usb_key>

The system becomes very unresponsive. X is almost completely unusable, maybe you can move a mouse for some time but click do nothing. Even togling the Caps Lock doesn't do anything. Trying to SSH is also almost impossible during this. System is like this all the time while using the dd command. After it finishes system again becomes responsive. I've noticed this on two of my computers:
1: AMD Athlon 64 3000+, 2 GB of memory, kernel 2.6.38.2
2: AMD Athlon II P320 Dual-Core, 4 GB of memory, kernel 2.6.39-rc2 The USB key is this one:
http://www.takems.com/products.php?categ=usb&prod=MEM-Drive_Easy_II

What I expected was that the doing dd wouldn't have a noticable impact on responsivness of the rest of the system.