Linux
Everyone where I work runs linux to admin linux servers. It's ace.

sed, awk and grep are fantastic. It takes me about 15 seconds on the command line to turn, say, a log file into a CSV file containing only the fields I'm interested in. Another minute or so (again on the command line) to make a graph and push it to a web server for someone to look over.

People really do underestimate how powerful the command line is. Sure, it probably takes a good few hundred hours to learn how to use it properly but you can get the basics within 5-10 hours and save yourself tons of time in the long run.

Have a look at:
www.commandlinefu.com/commands/browse/sort-by-votes

For some examples.

For the geeks: Oh, yes, GNU, etc. blah blah blah
(Toucan - http://www.titmonday.com, Wed 30 Sep 2009, 10:55, 1 reply)

Quite right too.
Vista was the final push for me to move completely over to Linux.

I still use DOS at work (where I have no choice but to use windows) for things mention in the OP - batch renaming of files, quick searching etc...(I simply cannot work out how to make that search thing in Vista actually search - too many times have I used it to search for something and it to come back as say 'no files found', then do a "dir /s *.doc" or whatever, and viola! there's the file I was looking for.

Although I got caught out too many times typing "ls -l" so I put a batch file "ls.bat" in the path ;-)
(dchurch bah, Wed 30 Sep 2009, 13:53, closed)

You may be a fan of
cygwin.

It's a horrible, horrible hack, but if you have to use it then you have to use it. Gives you all the good GNU stuff under Windows.
(Toucan - http://www.titmonday.com, Wed 30 Sep 2009, 13:57, closed)

I have
toyed with cygwin, but I could never get it installed using my Vista box. Constant errors for some reason. I gave up - this was an early(ish) version of Vista though, so I may try again.
(dchurch bah, Wed 30 Sep 2009, 14:03, closed)