Some stats from the last eight months. These stats come from the SharpToolbox web site, so this is really just about techies' habits.
March:     | IE | 55.6% | 
  | RSS aggregators | 38.6% | 
  | Mozilla | 4.6% | 
  | Opera | 1% | 
April:     | IE | 55.1% | 
  | RSS aggregators | 38.8% | 
  | Mozilla | 4.9% | 
  | Opera | 0.9% | 
May:     | IE | 47.7% | 
  | RSS aggregators | 46.2% | 
  | Mozilla | 4.8% | 
  | Opera | 1% | 
June:     | IE | 54.3% | 
  | RSS aggregators | 37.3% | 
  | Mozilla | 5.7% | 
  | Opera | 2.3% | 
July:     | IE | 54.5% | 
  | RSS aggregators | 35.6% | 
  | Mozilla | 7.8% | 
  | Opera | 1.7% | 
August:     | IE | 54.4% | 
  | RSS aggregators | 35.6% | 
  | Mozilla | 8.4% | 
  | Opera | 1.3% | 
September:     | IE | 52.3% | 
  | RSS aggregators | 38% | 
  | Mozilla | 8.2% | 
  | Opera | 1.3% | 
October:     | IE | 50.6% | 
  | RSS aggregators | 38.5% | 
  | Mozilla | 9.4% | 
  | Opera | 1.2% | 
 I wouldn't consided those numbers all that reliable, but I guess it's easy to see where developers are going :-)
 Update: on the search engine field, it looks like Yahoo is getting close to 6%, MSN close to 3%, while Google remains at more than 90%.