To increase the distance between an itemize item and the text:

\setbeamertemplate{itemize item}{\rule[0.5ex]{0.5ex}{0.5ex}~}

To make description items bold:

\setbeamertemplate{description item}{\textbf{\insertdescriptionitem}}

Nicer blocks with rounded edges and a bold title:

\setbeamerfont{block title}{family=\bf}
\setbeamertemplate{blocks}[rounded]