Semantic Web...? Let's be dirty from the nutshell. Nothing to freak out. Semantic means meaning of what we mean :). Suppose you want to search a country but you can't remember the name. But of course you know some facts of social, economic and geographical backgrounds. What if you type all the information you already know on google's text area. Will it be able to give you the exact country at once or will it search through every possible combinations and grant you thousands of results in which many are useless for you. Yet google is not that much of brave enough to deal with that kind of semantic mapping procedure as a background thread.
But certainly you may have seen if you type a single word and google it, there are suggestions appears bottom of your result page. Suppose the word is "Srilanka" then you may see a result like below.
Here they have treated the word Srilanka not just as a syntax of a web page but an additional added weight to gain its meaning as it is. Search Engine has been able to identify that Srilanka is a country and hence it is suggesting you to do following related searches also if need, like "srilanka map", "srilanka news" etc. Though you see it every day, did you simply ignore it or didn't want to go further with it or thought as this is also a kind of ordinary query searching methodology.
Of course this is some what like alpha version of semantic SE and this will not appear if it is not just a single word. The issue is, google is pretty much considering about their query retrieving performance and so when it comes to several words underline process complexity goes wild and therefore time consumption gets increasingly high.
How ever there are several semantically semantic search engines. "hakia" is a one such and you can make use of it via www.hakia.com. Hopefully there will be an another rat race of semantic era.