Vomit comes from gastric acid, right? And in gastric acid there is HCl and HCl is corrosive (strong), how come when I vomit, it doesn't destroy things that it (as the vomit) hits (such as floor, table)?
First of all, it is corrosive. People which are bulimic often get problems with their teeth getting damaged by the permanent exposure to the acidic stomach fluids. See the paper for more information:
Then it is a matter of concentration. According to Wikipedia, the concentration of the acid in the stomach is around 0.5% which is a pretty low concentration. Additionally the acid gets diluted when you eat or drink things. And last but not least not all things are very susceptible to a fast degradation by acids. Thing tend also not to disappear suddenly, if they come in contact with acids.
As Chris said it's a matter of a low concentration for a small amount of time. Most people clean up their vomit rather than leave it to sit. Most people who vomit also have recently eaten something which triggers the reflex but also dilutes the acid or may neutralise it.
To further add to Chris' answer. Even heartburn or gastro-oesophageal reflux disease, is particularly corrosive. Damaging cells that line the oesophagus, it causes changes in the cells that make them pre-cancerous (Barret's oesophagus) and can lead to full blown cancer (carcinoma). This is because the cells change type to try to protect themselves.
Even in the stomach a thick layer of mucus is required to prevent the stomach from eating itself. This is not only to protect the lining against its own acid, but the enzymes which are made are seriously dangerous and will digest our body if able, only work in acidic environments. To understand how dangerous they are, when the pancreas which makes these enzymes is blocked releasing these enzymes it can digest nearby structures such as major blood vessels and cause seriously dangerous bleeding.