A common meme from supporters of a certain candidate is that Obama is "fading." Let's look at the polls compiled here
http://www.realclearpolitics.com/epolls/2008/president/us/democratic_presidential_nomination-191.html#polls I will list the last three national polls from particular polling organizations. His support has in fact been very consistent.
Rasmussen
5/14-5/17 25%
5/07-5/10 33%
4/30-5/03 26%
Faux News
5/15-5/16 20%
4/17-4/18 20%
3/27-3/28 18%
Cook
5/11-5/13 24%
4/27-4/30 24%
3/29-4/01 17%
Gallup
5/10-5/13 26%
5/04-5/06 23%
4/13-4/15 26%
ARE
5/09-5/12 22%
4/09-4/12 24%
3/02-3/05 31%
CNN
5/04-5/06 24%
4/10-4/12 26%
3/09-3/11 22%
NBC/WSJ
04/20 - 04/23 31%
03/02 - 03/05 28%
12/08 - 12/11 18%
Pew
04/18 - 04/22 24%
03/21 - 03/25 26%
11/09 - 11/12 23%
ABC/Washington Post
04/12 - 04/15 20%
2/22 - 02/25 24%
01/16 - 01/19 17%
CBS
04/09 - 04/12 24%
Time
4/05 - 4/09 26%
3/23 - 3/26 24%
3/09 - 3/12 26%