I use currently (won't last) both Linux Mint 12 (32 bits) and LMDE 64. Gnome on both. Never had any problem with Sigil. I always downloaded the binary from Code.Google.com
My two cents.
If you look for a EPUB converter, I would advise LibreOffice and its extension
writer2xhtml which are opensource, multi-platform and efficient.
This is worth many $