Well, my font manager isn't as clever as I thought it was. I just realised that it's storing a new texture in the texture manager for each text item on screen, not once for the font object. So I'll have to look into that.
I'm not convinced this will work too smothly to be honest. The texture gets updated whenever a new glyph gets added to it, which means re-adding it to the texture manager, which is pretty expensive to do (Locking a static texture). So it'll have pretty bad performance initially, but should get better.

So, it looks like I'm going to be writing my own font loading code too. I was going to do so anyway, so I can do bitmap fonts, but I didn't reckon on writing a TTF renderer too. Although if I do, I can overlay textures on TTFs too. Which could be nice.

Anyway, it's low prioriry just now. ID3DXFont will do just now.