This is going to seem nitpicky, especially since these "not held by a Democrat since ____" (or a Republican in the case of parts of NY-23) posts are just a stand-in for what everyone already knows: The North and South are realigning, and have been for almost a century.  But I'm a political geography geek, so I feel compelled to point out that people seem to be misstating when Alabama's Fifth Congressional district was last won by a Republican.  In particular, bloggers seem to be relying upon this wikipedia entry showing a Republican holding the district in 1869.

In fact, the present Fifth as we know it has <i>never</i> been held by a Republican before.  Here's the history.  In 1869, Alabama's districts looked like this:

As you can see, nothing like the present Fifth even existed at the time.  The North was split up between two districts, and they were held by Democrats: Peter Dox and William Sherrod.

In 1872, Alabama added two Congressional districts, but made them at-large seats.  The state didn't redistrict until the 1876 elections.  At that time, it created a district bearing a strong resemblance to the present Fifth, numbered the Eighth.  Note how the less pro-Confederate northern portion of the state (Winston County actually seceded from the Confederacy) is divided up into three districts, and how the heavily African-American west-central portion of the state is sliced up between four districts.

It stayed the Eighth until 1972, when Alabama went down to seven seats.  It was then renumbered the Fifth.

A Greenbacker won the district in 1878 and 1880, and there was a close race in 1882 where the Republican got 48 percent of the vote.   Republicans typically won around 40 percent of the vote throughout the rest of the 1800s -- a very high portion for the South -- but between 1900 and 1986, a Republican never got above 25% of the vote.

The interesting thing about the Fifth was that it actually produced some of the more liberal Alabama politicians -- segregationists to be sure, but Democrats with a more populist streak like John Sparkman.