This problem did not occur in the 3.0 alpha, only in the newly released 3.0 beta1.
When trying to install plugins via Dashboard > Install Plugins, I get the following error:
Downloading install package from http://downloads.wordpress.org/plugin/google-sitemap-generator.3.2.3.zip…
Unpacking the package…
Fatal error: Allowed memory size of 100663296 bytes exhausted (tried to allocate 24715 bytes) in /home/plate2/public_html/wp-includes/formatting.php on line 1216
In the above case the plugin is Sitemaps but I have tried loads of different plugins, same Fatal memory size error every time.
The usual solution to an error like this would be to define a higher memory limit in wp-config and/or in php.ini and, actually, I do both as part of my standard installation, usually 96MB.
This error is occurring in both fresh installations of 3.0b1 and installations upgraded from 2.9.2 and 3.0a, all previously handing plugin installation and automatic upgrades successfully.
All my remaining non-3.0b1 installations continue to work smoothly, so, I don't think it is a problem with my server settings, something seems to have changed between the alpha and the beta.
Is anyone else having this problem with 3.0b1?