Jon Stewart at least used to apply satire to both parties, but lately he's degenerated into turning his entire show into trying to criticize anything remotely conservative or republican. It used to be funny because his political attacks would comprise maybe 5 minutes of his show at most, but now it's like 20 min of liberal blathering and 2 minutes of a guest who then takes his turn complaining about Pres Bush. Boring.
Colbert used to be funnier especially with him pretending to be hard-core conservative even though he's just as liberal as Stewart, but his show has also degenerated into a liberal complain and attack-fest. He barely pays lip-service to his schtik about pretending to be a conservative before he starts going after real conservatives and any republican that has grabbed his attention.
Another thing that has been disappointing with those two shows - they used to find stuff that the mainstream media had missed, and brought it up to discuss it and poke fun at anything ludicrous. Now, they seem to mostly just continue whatever the mainstream media is talking about except they make mean jokes about it.
It used to be funny but it's nothing but a liberal complainfest now. Even Limbaugh is more interesting now because at least he tries to be original and to find stuff that is mostly below the radar. And Limbaugh has the guts to criticize his own party based on his principles instead of just pick pick picking on one person show after show. He mixes it up from show to show, and that's far more entertaining than the same old same old you get from Stewart.
The day I quit watching both the daily show and the colbert report was only a few weeks ago... I tuned in about 5 minutes into the daily show and got 20 minutes into the show before I realized it was a re-run. Stewart is such a broken record (repeating himself every show) that I simply couldn't tell the re-runs from the new shows. Colbert was the same, saying in one sentence "hey I"m a conservative!" and the next sentence repeating some stale joke about Cheney shooting someone from his underground bunker. Stale. Boring.
Watch for a week or two, and you'll probably see the same thing - they jumped the shark about 3 months ago when they decided to become vocal critics of one side of this year's presidential election. It's not comedy, it's a daily political attack ad.
Last note - Jon has become increasingly bitter this year. Look closely at his facial expressions and listen to the tone of his voice. He really is bitter and angry. Not funny anymore.