As stated before, are you able to make and receive calls and are you dropping calls.
If neither of the above are happening than I wouldn't really be worried. Now if you are in a strong coverage area and you are unable to make calls and calls are dropping, than that is the time to be concerned.
I personally never look at how many bars I have, unless I am out in the boonies, and even than I place a call and wait to see what happens.
Call bars can be effected by the software in the phone, so if the software is glichy it could affect how many bars are on the phone.
So how many signal bars can be affected by the phones software. If a phone manufactuer wanted bars measured by just signal strength from a tower they would show more bars, than a phone manufactuer who had the bars displayed by signal strength from the tower and also taking into account congestion from the tower, which could show lower bars than the previous method.
For CDMA you should also see the same clarity with 1-4 bars, most of you voice quality decline with respec to bars was for analog signals and should really affect digital.