(Try this 2006 CRS report for background.)

In fact Tiarht, as a rider to the Commerce apps bill (where ATF get their dough), has been around in varying forms since the FY03 bill (which was the omnibus H J Res 2 (108th)) - though (the CRS report says) Tiahrt only got in on the act with the FY04 bill, in the full committee markup.

The current version of the rider is, I assume, the one in the FY06 bill HR 2826 (109th). (I say that because FY07 was dealt with by continuing resolutions, which - more assumption - would have carried forward FY06 riders.)

One key element (at one stage, at least) was the effect of Tiahrt on civil litigation against gun manufacturers - apparently ATF traces have been important evidence in some of those cases.

Who were the guilty senators who voted for Shelby?

I can't be arsed to track down the NRA scorecards: the Brady Campaign version suggests likely suspects. (It's only updated to the 108th - but a subsequent change of heart is surely unlikely.)

The list of members has as low-scorers Leahy, Dorgan and (the lowest of the low!) the NE Nelson. (Bobby Byrd scores highly.)

On the side of the angels, the mayors (Brer Bloomberg not the least of them) are pushing for a rollback of Tiarht.

(Mikulski, as chairman of the Commerce apps subcommittee, was, according to this piece from June 25, going to ditch Tiarht in her chairman's mark of the bill.)

I get no sense that this issue exactly has the lefty sphere riled. Not like something really earth-shattering like - Ann Coulter getting bitchy...