Google has started Considering the Load Time as an Important Factor while Ranking a Website at Index time.

Common reasons for a site to get load slowly.

The Time For Loading A Web Site Depends Mostly On:

1. The number / size of external resources included in the site.(Images , Feeds)

2. If Images are not properly optimized and resized. (Large and Heavy Images)

3. The database queries executed while the site loads. (Many database queries at the same time)

4. Use More Flashy Effects and High Resolutions Images. (If Flash has been used with heavy images)

I Hope This Information Helpful For You All.