As the new session of Congress begins, Senate Democrats are making a concentrated effort to reform the filibuster. Following the November elections, which reduced the Democrats' seat advantage in the Senate to 53-47 (including independents Bernie Sanders and Joe Lieberman), every Senate Democrat signed a letter to Majority Leader Harry Reid committing to filibuster reform. While the specifics of any such reform have yet to be established, it's clear that Democrats are convinced that the Senate rules must be changed to prevent the delaying tactics used so effectively by Republicans in the last Congress.
Reforming the filibuster could do much good for the functionality of the Senate, but it could also lead to strategy headaches for the Democrats. There are two central reasons for this: first, it could set an uncomfortable precedent for the setting of procedural rules in future Congresses; and second, Republicans would have more opportunity to pass their own legislation with only a few Democratic defectors.
Under normal circumstances, there must be a 2/3 majority vote in the Senate to change any of its operating rules. However, these rules are re-established at the beginning of each new Congress by a simple majority vote. Thus, the Democrats have an opportunity to change the rules now, without needing any Republican support to do so. The problem with this is that if the Democrats reform the filibuster without any Republican votes, the Republicans can (with some justification) claim that this is merely a partisan maneuver. This would give the Republicans grounds to modify the Senate rules however they like the next time they're in power. If, instead, the Democrats decide to negotiate with Republicans in an attempt to make the changes bipartisan, whatever alterations might be made will likely be far less beneficial.
The second issue has been much less discussed in the media, but could cause more problems for Democrats. In the new Senate, the Democrats will have a much slimmer majority than they enjoyed previously. It would take only 4 Democratic defections on any given vote to give Republicans a majority. Since the Republicans have proven far more adept at keeping their caucus together than the Democrats have, it is well within the realm of possibility that Republicans could get conservative Democrats such as Mary Landrieu, Ben Nelson, and Max Baucus to join with them in passing conservative legislation.
Because they control the House, Republicans could conceivably pass such bills as the health care reform repeal, leaving it up to President Obama to veto any such bills. It is unclear at this point how willing to use the veto pen the President will be. In the last Congress (which was, of course, controlled by Democrats, and thus produced more progressive legislation), Obama vetoed only 2 bills. His emphasis on bipartisanship and non-confrontation over the past 2 years suggests that he may be reluctant to stand up to Republicans and veto legislation, except in extreme circumstances. The health care bill is probably safe, but measures such as a further restriction of abortion rights or any cuts to programs such as Social Security may be harder for the President to veto, unless he decides to take a much more confrontational stance with Republicans than he has so far.
All this depends on the specifics of any changes. Some of the possible filibuster reforms which are being considered include ending the practice of secret holds (by which a single Senator can hold up legislation without identifying himself) and eliminating Senators' ability to filibuster the motion to proceed on a bill. These changes would eliminate much of the red tape and delay which prevents legislation from being passed in a timely manner.
Possible changes to the rules for filibustering the final vote on a bill are still being suggested, and ideas put forth so far include putting a time limit on any filibuster, changing the number of votes required to break a filibuster (perhaps to 55 instead of the current 60), or shifting the onus to the obstructing party on votes (in other words, making it so 40 Senators have to be present to vote "no", rather than 60 voting "yes", or else legislation proceeds to a final majority vote). Until we know more specifics about what changes the Democrats will make, it's difficult to know what effects filibuster reform will have, but it would be wise for them to make sure that any changes to the rules don't give the Republicans more leverage in the Senate than they already have.