Changing default width of blocks in LaTeX Beamer

Use p{width} for your column specifiers instead of l/r/c.

\begin{tabular}{|p{1cm}|p{3cm}|}
  This text will be wrapped & Some more text \\
\end{tabular}

EDIT: (based on the comments)

\begin{table}[ht]
    \centering
    \begin{tabular}{p{0.35\linewidth} | p{0.6\linewidth}}
      Column 1  & Column2 \\ \hline
      This text will be wrapped & Some more text \\
      Some text here & This text maybe wrapped here if its tooooo long \\
    \end{tabular}
    \caption{Caption}
    \label{tab:my_label}
\end{table}

we get:

As seen in beamerbasetheorems.sty:

\documentclass[notheorems]{beamer}

\theoremstyle{plain}
\newtheorem{theorem}{\translate{Theorem}}
\newtheorem{example}[theorem]{\translate{Example}}

% or

\theoremstyle{definition}
\newtheorem{theorem}{\translate{Theorem}}
\newtheorem{example}[theorem]{\translate{Example}}

% or

\theoremstyle{example}
\newtheorem{theorem}{\translate{Theorem}}
\newtheorem{example}[theorem]{\translate{Example}}

Whatever style you like. You can also change the appearance of the [alert|example]block:

\setbeamercolor{block body}{fg=blue,bg=white}
\setbeamercolor{block body alerted}{fg=blue,bg=white}
\setbeamercolor{block body example}{fg=blue,bg=white}

(Not tried it, just looked into the beamer sources)

EDIT: Still not sure want you want to do, but you can define your own theorem styles:

\makeatletter
\def\th@something{%
  \normalfont % body font
  \def\inserttheoremblockenv{alertblock}  
}
\theoremstyle{something}
\newtheorem{warn}[theorem]{WARNING}
\makeatother

\begin{warn}[Attention please]
This is dangerous
\end{warn}

(This works, I tested it)

You have 3 predefined blocks which you can customize using \defbeamertemplate. Look into the sources and the documentation on how to do this. If you need more block environments, see basebeamerlocalstructure.sty:

  \newenvironment<>{alertblock}[1]{%
    \begin{actionenv}#2%
      \def\insertblocktitle{#1}%
      \par%
      \mode<presentation>{%\usebeamerfont{block}%
        \setbeamercolor{local structure}{parent=alerted text}}%
      \usebeamertemplate{block alerted begin}}
    {\par%
      \usebeamertemplate{block alerted end}%
    \end{actionenv}}

Hope that helps