The concept of amnesty is bad, and almost everything in the Senate's illegal immigration amnesty bill is bad as well. It's fairly obvious to just about everyone that this is an extremely flawed piece of legislation, so what I'd suggest is using it to further discredit its supporters. However, please don't lose sight of the forest: we need to stop amnesty in general, not just this particular piece of legislation. You can do that by following these steps.

There's a top ten list in "Rewarding Illegal Aliens: Senate Bill Undermines The Rule of Law".

There are seven more reasons here, including the provision regarding the "United States-Mexico Border Enforcement Review Commission". I actually scanned that section earlier, but I failed to note this:

Members from the law enforcement community will be balanced out by members from "academia, religious leaders, civic leaders or community leaders" (read: the open-borders lobby).

For an example of how that would work, note that Illinois governor Rod Blagojevich's "New Americans Immigrant Policy Council" includes an organization which is headed by someone linked to the Mexican government (Juan Salgado).

David Frum has also discussed the downsides. In this post, he discloses that Bush has apparently never heard the pro-enforcement side of the argument. No big surprise there. And, from this:

With this immigration bill, the GOP is telling hard-pressed workers: Go look to somebody else to help you... ...the deal also identifies the GOP as a party that in the crunch puts employers' interests first... ...The president and the senators have now managed to divide and demoralize their party even further... ...The deal has wounded all three of the GOP front-runners... ...this White House's first instinct when faced with dissent in the ranks is to insult and abuse its strongest supporters... ...And unfortunately the White House's second instinct when confronted with dissent is to revert to incompetent spin. Unlike the Clinton administration, which lied with a fluency and bravado that will impress PR hacks for decades to come, the Bush administration stumbles, flusters, and eventually disheartens even its staunchest supporters... ...Republicans have done so well because until now, the highly diverse Hispanic population has not voted as an ethnic bloc. Now we ourselves are forcing that to change. It's as if this Republican president and these Republican senators have said, "Hmm. Can we invent an issue that will teach Cuban-American doctors, Honduran day laborers, and Mexican-American army officers to think of themselves as a unified ethnic group? Can we then provoke a fight that all of them (whatever their diverging practical interests) will treat as a symbol of acceptance in American society? And can we then stage-manage this fight to ensure that two-thirds of our party will have no choice but to fall on the wrong side of it?"

And, Hugh Hewitt - often described here as a Bushbot - has done yeoman work by reading the bill and posting several of its downsides here.

There's an online version of the bill here.

National Review calls it a "Bipartisan Fantasy".

And, Heather Mac Donald says "Don't Be Fooled", highlighting the provision that grants immediate legitimacy to former illegal aliens.

UPDATE: Sen. Jeff Sessions says "Immigration Bill Is Worse Than You Think".

UPDATE 2: Some of the downsides are in this segment from the Lou Dobbs show. Apparently illegal aliens would have first dibs on federally-funded legal aid for their applications for citizenship.