Most of our local stations went digital last month... I picked up a converter at Best Buy for about fifty bucks and it works great. The signals that were 'snowy' now come in clear as a bell.
Our flat screen is not HD, but on a 19" screen even the digital signal at 480i is great. Much better than the old analog signals. From my experience, HD only makes a significant difference on sets about 26" and larger.
Alan Jarand