There are currently (since a couple of weeks ago) two ways to get 'related articles' in HubMed: the first uses the NCBI's eLink service, so it's the same as the 'related articles' link in PubMed; the second picks out terms from the abstract of the original article and uses them to query a Lucene index. You can choose which method to use with the [pubmed/lucene] links near the top-right of the page. It's hard to say whether either method is better, but you might find something useful from one method that doesn't show up with the other.
I mention this now because of a paper from the NLM which describes using 'related articles' to assess a MEDLINE indexing tool that uses natural language processing to extract terms from abstracts.