I would suggest googling "TinyUmbrella," downloading it, and saving your SHSH blobs for 4.3.3 (that would be the only blob you can save now). If any further updates are released for iOS 4, download TinyUmbrella again, and save the blob for that firmware. If you have the blobs saved, then if you are not satisfied with the performance of iOS 5, you can downgrade back to 4. You need to do this now, before iOS 5 is officially released. Once Apple releases iOS 5, it will stop issuing SHSH blobs for older firmware, which prevents you from downgrading to an earlier OS.