If today's semicha is only an "echo" of the true semicha which ceased with the loss of the sanhedrin then
When a person doesn't have Smicha, he can't do anything that requires a Beis Din (a Jewish court).
Therefore, technically we shouldn't be able to
Hillel II (who was an Amora in the middle of the Gemara's time) was mekadesh all Roshei Chodoshim until the coming of Mashiach.
With regards to the other cases which require "real smicha", people with "real smicha" have already appointed us as "emissaries" for certain things. Therefore, we can judge cases that are:
Cases which are not common (like people punching people) or don't involve monetary loss (like fines) are impossible to judge nowadays. [Even though this is true technically, a court has the right to go beyond the law if they must. Since there are no truly ordained Rabbis nowadays, they would judge all types damages and thefts).
The Aruch Hashulchan says that conversions and divorces are considered like something which "causes a loss" as people would be prevented from coming under the wings of the Shchina, and women would be stuck (respectively).
source: http://hebrewbooks.org/pdfpager.aspx?req=9103&st=&pgnum=7
As stated by Vram, we still give it because it provides a useful institution for "certifying" knowledge of the various parts of halacha. We even have different types of smicha for different applications; yoren yore vs. yuden yuden, for example.
The premise of your "gneivas da'as" comment is that, due to the similarity in name, people would think they're identical. This is a difficult position to take, because you would have to prove that the expected type of smicha nowadays is for someone to receive "true" smicha. I do not think anyone would expect that, given that it hasn't existed for hundreds of years. Furthermore, those who are not aware that it is gone are unlikely to have ever realized it existed in the first place, and their concept of smicha is solely based on the current product.
There are probably numerous practical differences, but the main one I'm aware of is that we cannot form a true sanhedrin of 71 using the current brand of smicha; only those with "true" smicha can form such a beis din.
There has to be some way of demonstrating who is reliable.
Genevat da'at, based on the Gemara in Hullin 94a, is when someone thinks you did something contributory (or thinks you are willing to do something contributory) for their sake when really you didn't (or aren't willing to). Being uneducated isn't the same as falling victim to genevat da'at.
Semicha enables one to interpret torah shebe'al peh and legislate takanot (Rambam Hilchot Mamrim Ch.1) For example, if we had semicha today we could do away with a second day yom-tov outside of Israel. A Rabbi without semicha can only interpret the talmud (or nowadays the rishonim and acharonim). (As for point 3, the other answers probably address that more comprehensively.)
