WordWeb Online

1. Used in negative statement to describe a situation that has existed up to this point or up to the present time
   "So far he hasn't called";
   - thus far, up to now, hitherto, heretofore, as yet, yet, til now, until now
    
2. To the degree or extent that
   "so far as it is reasonably practical he should practice restraint";
   - insofar, in so far, to that extent, to that degree
    
3. Used after a superlative
   "this is the best so far";
   - yet

Encyclopedia: So far, so good