The Chicago Reader's Ben Joravsky has a sympathetic portrait of an Illinois Green Party candidate up, in an article about the way the two parties muscle third parties off the ballot.
Just to be on the safe side, [Green candidate Kathy] Cummings submitted 3,494 signatures to the Chicago Board of Election Commissioners on June 26. The Democrats quickly counterattacked: on July 3 Guadalupe Miranda, Soto's secretary, challenged the veracity of 2,440 signatures on Cummings's nominating petitions. To help push the case, Michael Kasper, the state Democratic Party's election-law wizard, was brought in.
For the first round of the challenge–the so-called binder check–Kasper, Cummings, and a hearing officer sat in a warehouselike room in a downtown county building for about a week, reviewing hundreds of nominating petitions. According to Kasper, the majority of the signatures on Cummings's petitions failed to match the signatures on the voter registration cards. He convinced the hearing officer to knock just shy of 2,000 signatures from her petitions and remove Cummings from the ballot.
This story could have been written in almost every state; every two years, connected lawyers make pretty good money purging third parties from the ballot (there are exceptions in states like California, where it's ridiculously easy to make the ballot). The most explosive case this year is in Pennsylvania, where the clever Rick Santorum campaign funded a dim-bulb Green candidate for Senate to help him on the ballot and spoil the chances of Democrat Bob Casey. (Pennsylvania wags tell me the Green will probably get pushed off the ballot anyway due to petition fraud.)
The Libertarian party is usually immune to the chicanery, for two reasons. One, the party is so well-established in most states that it doesn't need to constantly re-petition for the ballot. Two, it's rarely clear which party the LP is "stealing" from, so the parties don't risk propping up a spoiler. In Washington state's 2000 election, Republicans (like National Review writer John J. Miller) claimed Libertarian Jeff Jared had spoiled the election for Republican Slade "best senator's name ever" Gorton. This year, Republicans are hoping anti-war libertarian Bruce Guthrie will steal votes from the pro-Iraq war Democrat who won that year, Maria Cantwell.