NZBMatrix is dead but I wasn't going to let that keep me from USENET.
While waiting for the dust to settle and a new indexing service to bubble up I wrote my own quick and dirty indexer in Python with MongoDB on the backend. Get it here.
The indexer takes a list of newsgroups to crawl as an input parameter, and searches for NZB files within those groups. Any article it finds that has '.nzb' in the title gets recorded in the database. The crawls are time stamped so only new articles are grabbed on each run.
I've got it set up to crawl 10 of my favorite groups every hour which usually takes under 5 minutes.
Next steps are to take the retrieved NZB article fragments and build up the actual NZB file. That will take some tinkering with yEnc... and may never happen now that I've found a decent replacement for NZBMatrix: