hi,
>My partner and I are both "residents" expats. She is eligible for
> "permanent resident" status. Once she has it, does the partner also
> become eligible for PR status?
No
>If so, does this only apply to married couples or also people living
>common law? If only to married couples, if we got married, would it then
>apply? Or is there a waiting period?
Still no, but you can apply for depenadant visa
>If partner isn't eligible at all, are there still benefits? For instance, could
>PR partner sponsor other partner's visa (ie, if that partner not eligible for
>work visa)?
for a married couple - may apply for dependant visa, a dependant visa
does not entitle you to work, study, or conduct voluntary work
> Basically, the idea is one of us will get PR and we're wondering if any way
> to fasttrack PR for other partner (ie, rather than waiting for second
> partner to be here seven years). Getting married could be an option if
> that's a prerequisite, although otherwise we're not in a rush.
Makes no difference
> Have been living together for five years, unfortunately Hong Kong doesn't
> seem to grasp the concept of "common law" partners (or "basic law"
> partners

)
correct, however you could try if for example you had a wedding date set