The folks at Progress claim huge conversion rate benefits to EasyAsk, although unfortunately so far I’ve been unable to drill down and see what those numbers really mean. (Flagship customer = Land’s End.) Baynote makes more modest but still large claims. (Flagship customer = no big names that I’m aware of.) Endeca is clearly the market leader. (Flagship customers = Wal-Mart, Home Depot.) Mercado and Inquira are important players, at least in certain verticals.
I think it’s safe to say that e-commerce site navigation aids constitute a really important product category.