Is it even significant? If it's to be available end of April, will it be worth a premium when both nV and ATi are expected to announce new cards in May or June?
Still, someone had to be the first to sell a 512MB card, and a 6800U isn't exactly a bad card to strap 512MB to, especially in SLI mode. But I still consider it too much, too soon. The next generation of high-end cards should make 512MB look far more attractive.