This has been discussed here recently. The gist is that [itex]1^\infty[/itex] can only be interpreted as standing for a class of limit expressions, including the following:
[tex]\lim_{x \rightarrow \infty} 1^x = 1[/tex]
[tex]\lim_{x \rightarrow \infty} (1+\frac{1}{x})^x = e[/tex]
[tex]\lim_{x \rightarrow \infty} (1+\frac{1}{x})^{x^2} = \infty[/tex]
Since these don't all have the same limit (as opposed to, say, the limit expressions corresponding to [itex]0/\infty[/itex]), we can't assign a value to [itex]1^\infty[/itex].