I had the blank page of death problem when logging in to my blog after upgrading to 2.7.1. What this means is that after I logged in, I would just get a blank white page with no page source.
To workaround this, I was tediously moving the akismet directory or the plugins directory to login and then moving it back afterwards.
I finally fixed it by looking in the plugins/akismet/ directory and found an akismet_mmddyyyy.cache file and deleted it.
Lesson learned: Delete *.cache files in your plugins/akismet/ directory whenever you upgrade your WordPress blog.
UPDATE (2009-06-18): This problem happened again and I solved it by deleting any .* files in the plugins/akismet/ directory. Specifically, I found .akismet.bak.php and .readme.cache.php.