TinyUmbrella has been updated to allow you to save your SHSH blobs on iOS 4.2.1 for iPhone, iPod Touch, and iPad. If you are a jailbreaker and have 2 minutes to spare, I suggest you use it to save your SHSH blobs.
In case you don't know what TinyUmbrella is, it is a utility that allows you to save SHSH blobs, files that are necessary when you try to downgrade your iPhone to a previous iOS version. Without them, you couldn't downgrade. While most people don't care, it is especially helpful for jailbreakers...