It's starting to look like the Democrats will probably hang on to the senate seats in Colorado and Michigan. The latest polls show Mark Udall with a 7 point lead in Colorado and Gary peters with a 6 point lead in Michigan. Those aren't huge leads, but they are significant (exceeding the margin of error) -- and they show the Republicans still have a lot of work to do in those states.
Mississippi is another matter. While the Republican incumbent Thad Cochran holds a significant lead over his Democratic opponent (and will most likely win), there is an abnormally large number of undecideds in that race (about 31%). That's probably because Cochran's primary opponent (teabagger Chris McDaniel) has still not conceded defeat, and is fighting the primary result. If the teabaggers stay mad at Cochran (and either stay home or vote 3rd party in November), and Childers is able to whittle away a little at Cochran's lead, then this race could be a real mess by election day. This will be an interesting race to watch for the next few months.
The NBC News / Marist Poll in Colorado surveyed 914 registered voters, and has a 3.2 point margin of error.
The NBC News / Marist Poll in Michigan surveyed 870 registered voters, and has a margin of error of 3.3 points.
Public Policy Polling surveyed 691 Mississippi voters, and has a 3.7 point margin of error.