Having problems on two iPhone 4's running the latest version of cydia. Whenever I try to install an app from the mmi repo, it hangs for a bit and then I get the 'host unreachable' error.
At first I thought it was my wifi, but I get the same problem with 3G. I went as far as trying to restore my iPhone and re-jailbreaking because I thought it was a problem with my phone but no difference.