Just Do It
I think the biggest thing most people have to worry about is that they will discover there really wasn't anything worth watching in the first place :-)
There are going to be some hicups in the process, but delaying the transition will just delay the hicups. I think it is better to get them out of the way now, not later.
As for signal reception, if you have a good quality UHF/ VHF antenna already, it will still work. US DTV (which is not the same as HDTV) is using the same frequency bands as US Analog TV used. It's even using the same 6 MHz band width. It's not like you need a special antenna that is tuned to a different frequency band.
Having said that, there may be some minor confusion as the digital stations may not be on the same band (UHF, VHF) as they were before. Also, as many stations may switch frequencies/bands on Feb17 when they go back to running only 1 transmitter rather than two. In my local market, 3 of the VHF stations are on the UHF band for DTV. On Feb 17, two of them will switch their digital signal back to their old frequency (or at least band). The other will stay on UHF. Interestingly enough, in most cases, the decision as to switching back is being made a corporate offices, not at the local stations. To the end user, the biggest issue is that even with a DTV box (or DTV ready TV), they will need to re-scan for channels!
So what about US Cable? By law, the cable companies are required to continue analog broadcasts until 2011 (or maybe only 2010 -- I forget exactly). After that, it's anyone's guess. While people may complain at the cost of cable ($90+/month for digital cable), most don't realize that there are often much lower costs options if they push the person on the other end of the phone. In some markets, you can get the local broadcast stations (+ all of the shopping channels ever created) for < $10 / month.
IMHO, there are two groups of people who are going to have the biggest issues. The first ones are those who think the signal they are getting in their apartment from a connector on the wall is cable TV when it really isn't. In many apartment buildings, the signal is just the signal fed from an antenna (or antenna cluster) on the roof.
The second ones are the ones who had bad analog (NTSC) reception in the first place. Digital is not very forgiving: the signal is either readable or not. If the picture on your TV is full of "snow" now, you won't have a good DTV experience. (This reminds me of going from an analog cell phone to a digital -- my analog never dropped, it just got noisy. My digital cell phone drops.)