I’ve avoided weighing in on the topic of filibusters, trying to clairfy my own thinking on the issue. Now, I personally don’t have any problem with filibusters per se; if recalcitrant legislators can’t filibuster, they’ll find some other way to gum up the process (see, for example, the members of the Texas General Assembly who have apparently fled the state to deny a quorum to the Republican majority). But I do think the cloture mechanism is slightly broken.
At present, Senate rules require a 3/5 supermajority (or 60 votes) to end a filibuster. I think this requirement substantially reduces the burden on the supporters of the filibuster, as they don’t even have to show up at the quorum call for the votes; if nothing else, a filibuster should require some minimal effort among the disaffected minority to support it, but the present rules aren’t structured that way.
What I’d do: tweak the Senate rules slightly, to require 2/5+1 to vote to continue debate upon a call for cloture, except when a unanimous consent agreement is in effect otherwise limiting the debate (this part allows for normal floor debate without gratuitous cloture votes). That would properly place the burden of sustaining the filibuster on its supporters, but not otherwise limit its use (unlike Bill Frist’s fundamentally silly “supermajority countdown” proposal).