Ron Brownstein of the LA Times does the math and concludes that there's not much chance that the Democrats will retake the Senate in 2006.
Brownstein points out that there are more red states than there are blue states. Republicans hold 44 of the 58 red state senate seats and Democrats hold 28 of 36 blue state seats (six seats are in "swing" states). Moreover, the Dems are defending more seats in 2006 than is the GOP. The Republicans thus have more potential for gains than do the Democrats.
Of course, it might be asked why the Democrats should even worry about recapturing the majority as long as there are Republican senators like John McCain and his merry band who do everything possible to allow the Democrats to control things even when they're in the minority.
At any rate, there's a lot more interesting analysis in Brownstein's article. Incidentally, if he's correct and the Republicans hold on to, or even increase, their lead in the Senate, we expect a flood of editorials in liberal newspapers calling for amending the Constitution to allow for proportional representation in that body just as is done in the House. It rankles many Leftists that even though New York's senators represent more people than do the senators of many western states put together, each state gets two senators in Washington regardless of the population of the state. Thus a minority of small-state citizens can effectively neutralize the will of a large-state majority.
Call it "minority rights", of which senate Democrats should actually approve since they keep invoking the concept in order to justify the filibuster. Of course, the difference is that the right of small states to have the same number of senators as large states is fixed by the Constitution. That document is silent about any alleged rights of a minority political party.