[thelist] Redirect 301 a scary history - moving forward

[Rich Points]

Hi,
I started working on commerce about a year and a half ago.  This site 
has been around since about 1997 and has had numerous web masters.  When 
I took over there were many inconcintencies in file names and the 
extensions used.  So the first thing I did was to make all that stuff 
consistent by giving all the pages an .shtml file extension.  In 
addition I added a 301 redirect in the .htaccess file pointing the old 
addresses to the new ones. 

This seemed to work fine until last September, I don't remember the 
exact date, when Google danced and knocked many of the top keywords for 
this site off the chart.  Those keywords have bounced back but they 
still aren't as strong as they once were.

Now the client is moving to a new CMS and shopping cart system.  To do 
this will require another round of 301 redirects.  I'm very nervous 
about doing this as I know another drop in search rankings will drive my 
client and myself nuts.

Everything I've read about 301 redirects suggests that they work as 
intended. 

Here are my questions:

    * Was the drop that I experienced last fall just a Google thing or
      was it related to my redirects?
    * If I do another round of redirects would it be "safe" to get rid
      of the old ones which were first set over a year ago?
    * Should I gradually introduce the new redirects or do them all at once?
    * Any other considerations?

Thanks
Rich