Okay, that makes sense.
I have a 2011 MBP that came with Lion, and I'm about to replace the stock hard drive with a Momentus XT.
I'm guessing the best thing to do here is format a USB thumb drive (what format should I use?) and download a copy of Lion from the App Store to create a boot disk.
Since Lion came on my MBP, I should be able to download Lion for free right?
Get an external Hard drive enclosure (or a dock like I did). Seriously the easiest way by far to do this is to:
1) Connect the new HDD through USB in the dock (or external enclosure - though a dock is much quicker, you just pop it in!)
2) Use Disk Tools to format it (takes 30 seconds or less)
3) Your computer should now see the new HDD as an external hard drive
4) Load Carbon Copy Cloner and clone the entire internal HDD to the new one. (Depending on how full your current HDD is, it could take a couple hours... but you can see the progress on the bar...Mine took just over an hour for ~80GB worth of data.)
5) Carbon Copy Cloner will automatically make the new HDD bootable!!!!
6) Power down, remove the mag safe adapter, and swap out the HDDs (takes less than 10 mins even for someone who's never done it!)
7) Do SMC reset (plug in mag safe adapter, hold down shift-ctrl-option+power for 10 seconds then release all at once)
8) Power up as per normal but do a PRAM reset when it starts up (Option-Cmnd+P+R hold until you hear the boot chime twice then let go)
9) Your computer will boot as if nothing has happened!!! All your apps, settings etc will ALL be there as they were on your old HDD!! No need to reinstall anything!!!!
This really IS the easiest way to do it! two thumbs up for Carbon Copy Cloner!