You could already opt to receive email search updates from PubMed. If you have newsreader software on your PC you can now choose to have new references in your subject sent as an RSS feed.
To do this, run your search. Select RSS Feed from the Send To drop down menu. That creates a feed of your results, and you can then click an XML button to open that feed in a new window, with its own URL. Paste that URL into a news reader and you will be able to see new results for that search, as a news feed.
Each time a new reference matches your search, that reference will appear in the RSS feed. I use Klipfolio as my newsreader: this sits on my desktop and receives feeds from a variety of places including Nature, BioMedCentral (and the BBC sports site!). In the PubMed RSS feed, titles of papers appear, and if I click the title, I am taken to the PubMed abstract. I am happy to supply more details about Klipfolio if this is of interest.
There is more information in the NLM Technical Bulletin at http://www.nlm.nih.gov/pubs/techbull/mj05/mj05_rss.html