[thejeff]

Note that there is a large distinction between voter registration fraud and voter fraud.

ACORN has often been accused of voter registration fraud, but not, to my knowledge, of actual voter fraud. Like any voter registration group they are required to submit all forms they receive to the registrar. This is to prevent groups from throwing out all the voters that register Republican, for example. They can, and often, but apparently not always, flag suspicious forms. In at least some cases the election officials have ignored these warnings and later accused ACORN of registration fraud.

Registration fraud is usually caught at that level, especially when it's like the commonly quoted examples of cartoon characters and celebrities. Examples of people actually voting under these false ids, which would be actual voter fraud, are extremely rare in recent cycles.

What hasn't been rare are attempts to keep people from voting. Purging voter lists under various criteria intended to hit one party's area harder; Lack of voting machines, causing long lines and discouraging voters, in precincts likely to vote heavily towards one party, etc, etc.
These have the potential to swing far more votes than traditional voter fraud.