Of course I can't reproduce it now! However, about 20% of the time when I try to login to my Gmail account (because my wife is logged into hers), it gets stuck in an infinite redirect loop. I always end up surfing around to different Google sites for a while, and then eventually it fixes itself.
I found that it was the Smart Labels feature available in Labs that caused the infinite redirect loop. After using http://mail.google.com/mail/?labs=0 to get into my mail, I disabled that lab feature. After that, I could access email again normally. It's a shame this answer (specifically to use the labs=0 URL) isn't listed anywhere in the Google Apps help site.
I have the same problem on my Android phone when I log into 9 Gmail accounts. The last Gmail account X that I added always routes me to the first Gmail account Y. After reading this thread, I cleared all my cookies and then re-logged into X first. It worked! I then added most of the other Gmail accounts and all worked fine, but maybe it is because I now log into 7 Gmail accounts instead of 9. I didn't have the initial problem when I logged into 8 Gmail accounts, so maybe 8 is the maximum number of Gmail accounts you can log in on Android phones.