Since I was recently writing some Markdown and docu using TM2, I had decided to bump this thread. I blamed Apple for their bogus implementation of built-in spell checking, I still do. However somehow I find TM1 with that borked built-in spell checker pretty well, thile TM2 not so well.
Currently TM2 misbehaves (comparing to TM1): (1) document is not spell checked once loaded or when spell checking is being enabled (existing errors aren't marked)
I have spellChecking = 1 in my .tm_properties file, and this works very well for LaTeX projects. In particular, it shows errors that are already there when I load files, and highlights any new errors that I type.
Using the spelling settings in the menus doesn't seem to work very well though - and this is probably one of those "we recommend you put settings in .tm_properties files for the moment, as some things don't stick if you use the menus".
If you need to use different languages for different directories, there is a spellingLanguage setting too (language codes are here: http://pastie.textmate.org/private/xmwqhbzi8o9hdbhgcplw)
David.