After having successfully done it (not without problems), is it possible to just clone the memory card ie stick it in my laptop card reader and write it to a card reader in another USB slot.
There is nothing inherently wrong with doing that, but be sure to use a DD tool (same tool you used to write the card to begin with should work) rather than just a copy. Under windows/mac only the boot partition will show up.
And FYI if performance continues to be an issue you can set it up to run off of a usb key. (There are a lot of reports of the sd card being much slower than usb.) Just use the pi (or an extfs-capable computer) to create a new filesystem on USB and copy (or rsync) the sd root filesystem over, then change the kernel commandline to point to the new partition instead of /dev/mmcblk0p2 (/dev/sdXY where X is the disk number starting at 'a' and Y is the partition number, starting with 1. So it will probably /dev/sda1..)
That also gets around the core_freq SD corruption issues, as you can set the card to read-only (or not mount it at all by commenting out the /boot line in fstab) and overclock much farther.
I run my "general server" pi that way, OC'd to (non-warranty-voiding) 1ghz. The only drawback is having to pull the card to update the firmware.