Surface tension only applies to a compound in its liquid state, and Liquid metal is a solid by the time the knife is sold.
There was an article about this in Blade a year or so back. I remember the gist being that LM knives are composed of a chemical (as opposed to metal) alloy, and perform a lot like ceramic knives; their edge retention is considerably superior to most of the common super-steels (like VG-10 or S30V), but their impact resistance is dangerously low. Also, like ceramic knives, they are castable, but ridiculously hard to grind and ridiculously hard to sharpen. (Most of the few ceramic knives sold stated that the only way to sharpen the knife was to send it back to the manufacturer.)
There was also a sometime worry of beryllium poising, since liquid metal contains beryllium, but most of the people who know what they're talking about have dismissed it as a nonissue.
The knives around that are made from LM are supposed to be exellent slicers, but would not make good hard use knives becuase they just aren't that tough. Plus, while the edge retention is exemplary, the ratio of edge retention to ease of sharpening is outdone by many other proper steels.
As with ceramics, there's a reason the stuff never caught on.