It really depends on your hosting provider. My site is on a shared server and runs smooth as butter. I run a few relatively high-traffic websites (~2,000,000 page loads a month) on my portion of the server and there’s no issues. I’m also using some pretty big modifications, but as long as you get them from reputable places or code them well yourself, you won’t have a problem. A thing like Facebook share really shouldn’t effect your load times, unless the Facebook API load times are slow. This looks promising, but I never used it.
