Have you seen this yet? The new two-baht coins now have a golden hue, with subtle changes to the artwork.
According to the coin's entry on Wikipedia (geez, they have articles on everything), they were released on February 3rd.
The new metal is aluminum bronze, replacing nickel-coated low-carbon steel. Its info page on the Thai Treasury website provides further details: the aluminum bronze alloy consists of 92% copper, 6% aluminum, and 2% nickel.
The overall look of the coin is the same, with His Majesty the King on the obverse, and Wat Saket on the reverse. However, the artwork has changed subtly, having been redesigned for the new version of the coin. His Majesty's likeness is larger, and there are also subtle changes on the reverse.
The new coins were minted, as the Thai numerals show, in 2551, aka 2008. The Treasury website says the date the coins were announced (วันที่ประกาศใช้) is February 5, 2008. That's a full year ago--did they mean 2009, or there is a large gap between announcement and release into circulation?
When I first held the new coin, I thought it felt lighter than its predecessor. Turns out I'm not crazy -- it's 0.4 grams slimmer. I can't believe my fingers could detect that!
The two-baht coin is becoming more and more common. Introduced in 2005, the number minted has increased each year. In 2007, more than a quarter-billion were produced, bringing the total number of two-baht coins in circulation to more than 400 million.
I received these coins today as change at two stores located several kilometers apart, so I guess they've already been widely distributed. This is the first I've seen of them.