In terms of security, when the hostile agent gains access to a computer's console, all bets are off. Even if you had an EFI firmware password, a secure login on the OS and such, with dedication all can be cracked on the keyboard and ports. Only consolation is that most miscreants are not dedicated, knowledgeable or patient, so regular passwords do offer a modicum of protection.
As for installing Lion externally based on the stolen Mac's Recovery Mode infrastructure, I believe access to the registered owner's AppleID is required before Apple's servers welcome you in.
Unless you're a CIA/NSA agent with access to State Secrets, most thieves don't give a rat's furry arse for your iCloud stuff. What they want is the hardware in a reasonably operable state in order to profitably pawn it off.
If a thief is that technically skilled, then nothing will work to recover the stolen device.
I won't disclose the methods involved, it's better left unsaid on a open forum.
Recovery attempts after a item is stolen is almost futile, it's more meant to catch the low hanging fruit of new local thieves and act like a deterrent.
Most seasoned thieves use a fence which will use a geek to strip the machine and then it's sold overseas where it would be too expensive to bother attempting recovery. Then even if it was tried it would be some innocent who bought it off a friend who bought it off eBay, who bought it off a dealer, who bought it off a friend etc.
The costs involved to find the orignal thief would be horrendous, the machine likely damaged too.
Apple had a prototype iPhone stolen by one of their employees who "lost" it in a bar, they went looking for it once and never found it.
So the best course of action is being preventative, think like a thief and in public places consider any second a person has the potential to take your machine and run with it.
If at home, lock your precious in a safe. That's what I do (it's a big safe) because I know despite the alarms going off the burglar has enough time to grab something and run with it, the MacBook Pro would make a ideal selection.