The filibuster--the ability to indefinitely continue debate--is a Senate perogative, not a Constitutional requirement. Although the ability to filibuster has been in the Senate's self-adopted rules since 1806, the first filibuster was not made until 1841. Filibusters were rarely used before 1970. Even through the turbulent 1960s, it was unusual to have more than a handful per year.
The last session of Congress saw a stunning 139 motions for cloture filed. The current session is on a pace to meet that unfortunate record with 67 motions already filed. Prior to the last session of Congress, the highest number had been 82 motions, which occurred during the Republican-controlled Senate in 1995-6. These numbers understate the effect of the filibuster because legislation is often stymied by its threatened use.
The rules regarding filibusters are also not set in stone. Procedures were modified in 1975 to make it easier to filibuster (Senators didn't actually have to take the floor to talk) but also easier to invoke cloture (the threshold for closing debate was lowered from 67 to the current 60 Senators).
According to The Hill,
Under Harkin's bill, which is co-sponsored by Sen. Joe Lieberman (I-Conn.), 60 votes would still be necessary to cut off debate on an initial procedural motion. If senators failed to reach 60 votes, a second vote would be possible two days later that would require only 57 votes to cut off debate. If that also failed, a third vote two days after that would require 54 votes to end debate. A fourth vote after two more days would require just 51 votes.Sen. Harkin's proposal for multiple and repeated cloture votes provides an opportunity to extend debate. A minority of Senators who were concerned about a bill or nomination would have extra opportunities to convince their colleagues and the public of their case. However, a majority of Senators could eventually hold a vote.
Sen. Harkin's raises obvious partisan concerns. If it were currently enacted, it would take power away from the small Republican minority. To gain the necessary bipartisan support (67 votes are required to change the Senate rules), Sen. Harkin should make the rules effective for the start of the next presidential term--that is, at the start of the 113th Congress in 2013.