What it does
The most recent version, 0.5 (25 Jan 2008), supports multiple textures and URLs. You can create as many HTML textures as you need. The framerate, even with multiple Flash animations, is quite good.
The texture appears backwards in Unity, so you need to apply a placement transform of -1.0 in the X dimension. Textures dimensions currently must be a power of two (i.e. 256, 512, 1024).
How to use
Like other texture plugins, your code needs to create a new bitmap at the start, then call htmlTexture_start() with the ID of that texture. You then update the texture's pixel data every so often -- typically every Update() or FixedUpdate(). The sample below is C#: