I have a 24/7 AIS feed monitoring the western basin of Lake Erie from near Toledo OH. There are also some others around the Great Lakes, including one from near Duluth that's up all the time. Plus there are some others, one from Cleveland that's usually up the weekend, and on occasion near Sault Ste Marie. Also there are folks sharing along the St Lawrence Seaway.
See also a screen shot I have from a previous thread:
http://www.radioreference.com/forums/showthread.php?t=37656
From what I'm seeing, essentially all commercial ships and tugs that are coming in and out of my area are up on AIS. Also most Coast Guard Cutters have AIS, but not the smaller local boats at Station Toledo. Overall it proves to be entertaining and informative to visually track activity while monitoring marine channel voice traffic.
Also keep in mind compared to ACARS, all transmissions are from ground/sea level and only 12.5 watts, so more of a challenge but very possible to get a consistent range of 20-25 miles from my experience. When the weather and conditions are right, signals from much farther as possible.
My current setup is using an Icom PCR-1000 for the data signal and a custom 160 MHz ground plane antenna in the attic.
Also the ShipPlotter group on Yahoo provides additional support and discussion from the diverse pool of international users. Hopefully this will pick up more in the states and more full time feeds will be up and around the Great Lakes area.