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…
To use it, just download TinyUmbrella from here, plug your iPhone in, and click “Save SHSH”.
Better safe than sorry. No?