The only problem with AIS is that it requires electricity to work.... and electrical systems on small boats are not the most reliable in the world. That is also the problem with the Sea-me active radar reflector.
Unfortunately, that is not the only problem with AIS. Another big problem is that bridge crews do not always pay a lot of attention to it -- generally less than they do to radar. The early versions had a stand alone display screen that, while required to be installed on the bridge, often was tucked away in a closet somewhere. Many harbor pilots reported coming aboard ships and finding that the bridge crew on duty didn't even know where the AIS display screen was located, especially with foreign crews/flagged ships (it's a USCG-originated requirement, afterall.)
Newer AIS can interface with the ECDIS, which helps to get the info in front of bridge crew. But the information being displayed is confusing often enough that bridge crew tend to be skeptical of what they're reading. Examples of confusing information occur, for instance, when bridge crew neglect to update the ship's status line, so their AIS transceiver may be broadcasting that they are "quayside - Seattle" when they are actually steaming out of the Straight of Juan De Fuca.
As currently configured, AIS seems to be a greater benefit to HomeLand Security entitites, and business enterprises that track cargo shipments (e.g. http://www.aislive.com/
), than it is to commercial vessels or recreational sailors. But that will likely change as potential benefits of AIS are exploited by technology upgrades.
Here I must add a disclaimer as my company is involved in devellopping technology that aims to exploit the AIS network to greater advantage.