If your having Problems leaving comments on People Blogs...

...go here

Looks like the best thing to do is clear your browsing history and cookie cache (and reopen it to make sure its gone) then restart your browser.

Also uncheck the "stay logged on" tick box for the Google Blogger/ Gmail login screen.

I haven't been able to leave comments for ages, and now I can so it seems to work.  Apparently they are working on it.

Cheers
Jason