Certainly it has a steep learning curve but it has a very large community that supports its packages and now also has a friendly and helpful community http://tex.stackexchange.com/
They can be as friendly and helpful as you want, but that doesn't change the fact that the input format for mobi and epub is basically HTML; meaning that by utilizing TeX, you are basically adding another layer that doesn't provide much value. The beautiful fonts, formatting, spacing, etc.. etc... that TeX provides will all be lost on your ereader.