Question: I bought a 240 GB SSD to replace the 500 GB primary HDD in my new MacBook Pro.

How do I clone the current Lion system image on my 500 GB HDD to the SSD? I want to clone the entire drive not just copy data.

I can only have either the HDD or SSD in the MacBook Pro at a time. I have an external 500 GB USB drive that can I use if necessary. I've seen suggestions on using Carbon Copy Cloner but I'm not sure how to proceed with only one disk in the MacBook Pro at a time.

Answer: 
I am using the Migration Assistant on the old hard drive to migrate the data from a Time Machine backup to the new disk. It won't work for every situation (need USB enclosure, etc) - but it looks like it will work for me.
Ditch your optical drive and use a "data doubler" to keep your HDD in your MBP along with your SSD. I do this and keep all my heavy use files (OS, Xcode, ~/Library, Applications, etc.) on the SSD and then things like Movies, Music, and Pictures folders on the HDD. This way I can still buy a relatively small and inexpensive SSD but still have all the storage I need. When was the last time I needed to read a DVD? ha!

I got my data doubler here: <http://eshop.macsales.com/shop/drive_bracket/datadoubler/> and installed it myself pretty easily. Speed is now unbeatable and I still have endless storage.

As far as copying the data, I would make a disk image from your current hard drive to external using Disk Utility. Then use Disk Utility again to put it onto the SSD from external. Just keep in mind that you can't image a disk that you booted from, so you might have to install Lion onto the SSD temporarily to boot from while you create your image.