I'm in the process of narrowing down my choices for law school, and wondering if it's true that, generally speaking, only degrees from the top 20 schools (or maybe even only the top 15) are "portable" nationally?

I'm generally only considering schools within the top 30, but will limit myself to the top 20 if schools ranked from 21-30 are going to limit my ability to get a job outside of the city/state I go to school in.

Any insights/advice from you seasoned pros would be welcomed.

It's not a city rule, but more of a regional rule. For example, UC Hastings or Davis are marketable throughout California and in the West, but much less marketable in the South and NE. Emory is great all through the South, but garners little respect out West.

Regarding portability, AmLaw 100 Firms rarely dip below top 30 schools nationally and top 50 schools locally. AmLaw 200 firms (101-200) will generally take top 50 nationally and top 100 regionally and occasionally dip into the 3rd of 4th tier locally (mostly through laterals, not first year hires). Thus, going to 30-50 school limits you regionally with respect to big law and going to a 50-100 school limits you locally. If you are 3rd or 4th tier, forget biglaw and in all honestly, I wouldn't bother with law at all unless your driven by purpose (public defender, non-profit) and not money, because you'd have better odds in Vegas.