Yes, there are new fonts in Windows 8.
There is a blog post detailing the new fonts - Script and Font Support in the Windows 8 Consumer Preview.
Note that some letters of Segoe UI have been redesigned, as shown (source at MSDN):
In Windows 7: 
In Windows 8: 
The following table lists scripts newly supported in Windows 8, and associated fonts:
New scripts Script origin Fonts Comments on language usage -------------------------------------------------------------------------------- Glagolitic Europe Segoe UI Symbol Historic Gothic Europe Segoe UI Symbol Historic Old Hangul East Asia Malgun Gothic Historic (Korean texts) Old Italic Europe Segoe UI Symbol Historic Lisu China Segoe UI Lisu Myanmar Southeast Asia Myanmar Text Myanmar, Shan, Karen N'Ko Africa Ebrima N'Ko and other Manding languages Orkhon China Segoe UI Symbol Historic From the blog:
The UI font changes are as follows:
- Ebrima font: updated to add support for Ethiopic and NʼKo scripts
- Gadugi font: new font for Canadian Aboriginal Syllabics and Cherokee scripts
- Microsoft JhengHei UI: new font for Traditional Chinese script
- Microsoft YaHei UI: new font for Simplified Chinese script
- Nirmala UI: new font for South Asian scripts (Bangla, Devanagari, Gujarati, Malayalam, Odia, Telugu)
- Segoe UI (certain weights): updated to add support for Arabic, Armenian, Georgian (Mkhedruli), Georgian Khutsuri, Hebrew scripts
Some fonts have been updated:
Comic Sans gets a legitimate italic and bold italic - New Typefaces for Windows 8
Further sources: