The whole site is pretty interesting. I had heard a strange (and false) rumor that Lem had "disappeared" with the comment that his name was a pseudonym, and he'd only written SF to get his political ideas out while remaining under the Communist radar. With the dissolution of the SSR, there was no longer a need to publish under an assumed name or in the field of science fiction.
He seems a trifle prickly in a thoroughly Eastern European fashion, and he has been known to make less-than-admiring comments about US science fiction - apparently there was quite the flap with SWFA, and Phillip K. Dick wrote a letter about him to the FBI... Anyhow, I can see how the rumor might have come about. I'm just as happy to find it not so, however.