I downloaded the public beta to use with LR 3.4 on my MacPro 8-core, 32GB RAM.
It's actually a very nice program. It's easier to use than Photoshop so I think that it enhances the LR-only workflow. The results are very good.
That said, I already own PS CS5 so the idea of spending $160 on the Layers plugin is not justified for the few times that I need it. But it may be worth the investment if I don't see the need to pay for the next PS upgrade. That's unlikely for me, but for many LR-centric users, it may be a good choice.
You still end up with a new PSD file with the plug in. It would be much cooler if the program accomplished it's mission completely in metadata so that you don't end up with more giant files to manage. If that were the case, then I think more folks would buy the plugin, even those who already own PS.
Now if they add perspective correction as a plugin and combine it with the layers plugin, I'm a definite buyer. Just for the convenience alone.