Searching pairings on mugglenet fanfiction is a bit of a pain. You can only set it for pairings such as Harry/Ginny and Ron/Hermione. If someone wants a fic containing a pairing such as Sirius/Ginny or Hermione/Victor in the Other Pairings category. Personally I hate looking at hundreds of fics before even getting to a story which is remotely what you are looking for.
I agree with this suggestion. On a side note, maybe, like in the hospital wing's character section, you should be able to browse fics of all genres by specific characters. When an author writes a fic, like choosing a genre, they can chose a 'prime' and/or a 'secondary' character they focus on in their fic. I've seen this done on other sites, and it save a world of hassle if you want to read about a specific character.
We will investigate trying to implement this suggestion, it is a coding issue so it may take some time.
In the meantime, try Fiction Junction. You should be able to find recommendations for specific pairings.