I have been using Sigil 0.5.3 on a 32-bit Debian sid (actually aptosid) system for routine production work. It was installed from the linux binary install that you can still download from the Sigil download page (use "search all downloads").
Note however, that due to certain QT issues, Sigil does not play nicely with KDE from about KDE ver 4.6 up. Most things work, but for example you can't drag and drop chapters to change their order without crashing Sigil. This is true even if you build from source, in my experience.
If you're planning on using Sigil extensively, and especially going forward, you might want to consider Ubuntu, and set it up to build from source.
Of course, if you're using Gnome or XFCE or some other non-KDE desktop, you may be fine.