Shiira is the browser you'll love to hate. It has promise and some nice features (full screen browsing window is great for developers to showcase their sites to their clients), but it poorly maintained and rife with bugs which sadly makes it of little value.
The last thing you want is your browser to crash. It's right up there with your mail client throwing in the towel: infuriating. Sadly, Shiira is a really big let down in this department. It's always been far too unstable to rely on.
While the UI is very refined and the team have always pioneered an overall sexy design, ultimately it is just too flaky and inconsistent.
Shiira is more of a testcase than anything truly of value. It seems developers are using it to simply try out new code rather than make an actual product for mainstream consumption (or any kind of consumption for that matter). Everything is half done, like those people that love home repairs, but just can't seem to ever finish a project. That's what Shiira feels like. Things are implemented, but never truly finished.
All this does is give Shiira a pretty face, but not much else. A clunky backend and some half-baked ideas make it a novelty rather than a real piece of software you can fire up on a daily basis. A shame really. These are those rare programs that have always shown a glimmer of hope...