It's official (although never officially stated, that I know of):
Rosetta is dead and gone in Mac OS X 10.7 Lion.
I just finished an exhausting search to find any hopeful news of a workaround. After all! There's a workaround for installing Front Row, which was also killed in Lion. (See HERE for the Front Row fix). So why not Rosetta? If you scour through the Lion notes over at MacInTouch you'll find that there is nothing stopping you from installing Rosetta from a Mac OS X Snow Leopard 10.6 DVD. However, it won't work. The best explanation is that Rosetta requires PowerPC framework files from within the System, which were also deleted from Lion. IOW: There aren't any APIs for Rosetta to access. It's inert. It's a dead parrot. Why were the APIs removed? That's a matter of speculation. One guess is that Apple are preparing to allow Mac OS X to run on ARM processors, similar to iOS. (And iOS at this point is just base Mac OS X compiled for ARM with a different GUI on top). (Yes it is! Do your homework and don't argue with me kids. Sheesh. ;-)
If possible, you could pay for new versions of your applications. Apple left PowerPC CPUs behind in mid-2006. Maybe you should leave behind your old PowerPC apps at this point. But this often difficult or impossible. Some old PPC applications simply don't exist any longer. Or upgrading an app can be is EXPEN$IVE! Or stupid companies like INTUIT have been too lazy to drop their old PPC Carbon code and go to Cocoa Intel CPU processing code. (0_o)
What are the other options?
What I have found as one good alternative is to attempt running Mac OS X 10.6 Snow Leopard in VIRTUALIZATION via Parallels or VMware. 10.6 Server has been legally running in virtualization for a couple years with Apple's approved. According to its new license, 10.7 Lion client is now legally able to run in virtualization. So why not try running 10.6 Snow Leopard client in virtualization? I haven't done it yet. But if it works, that would be the quickest and easiest way to access Rosetta and the PPC apps it supports. Note that I am not saying this is exactly 'legal'. However, I don't personally expect Apple cares at this point in time.
Second Boot Partition
Personally, I've been using another alternative for years. I call it 'The Other Partition', or just as meaningfully 'The Other Volume'. For intermediate Mac users it's dirt easy to do. You repartition your boot hard drive to have TWO (2) partitions. You can boot from both of them as long as each of them have their own installed operating system. If your Mac hardware can run on Mac OS X 10.6 Snow Leopard, then why not install Snow Leopard onto one of the partitions?! Then custom install Rosetta onto it as well and all your Rosetta compatible apps will run on it. Install them all into the Applications folder on the Snow Leopard partition! You simply reboot your Mac with the Option key down, choose your Snow Leopard partition and GO!
Therefore, with a reboot, you can run all your oldie but goodie PPC/Rosetta applications. No, it's not convenient. It's merely FUNCTIONAL, which is actually what you want.
What else is a second boot partition good for? I've been using it to repair my main partition every month. It's far easier and more effective than running Disk Utility from a boot DVD. I can also run on it every other hard drive utility I own! That includes DiskWarrier, TechTool Pro, Drive Genius, blahblahblah. I consider it essential.
How do we set up this second partition?
If you're like me, you like to do a low level format of your boot drive every now and again anyway. So after the format, choose in Disk Utility to create two partitions.
Another utility to try is Drive Genius. It has a tool called Repartition that will allow you, if you have enough hard drive space, to add another partition to your already working boot drive. I suspect there are other such utilities as well for Mac.
Please share if you find other useful options for PPC application users running Lion!