
It is impossible to empirically measure how many jobs have been saved, so the "saved or created" numbers Obama uses are complete fabrications based on the White House's own shifting macroeconomic estimates. No matter how bad things get, Obama can always claim—without evidence—that things would have been worse, therefore he saved jobs. The gullible news media have been falling for it.
That said, the bulk of the stimulus package takes effect in late 2009 and in 2010, so we should not expect it to have had much economic impact yet.
Update: Someone pointed out to me that I forgot to specify the source of the graph. The specific version of the graph I posted came from Harvard economics professor Greg Mankiw's blog. The original graph came from this document by CEA Chair Christina Romer. The unemployment information plotted on the graph can be found on the St. Louis Federal Reserve web site.