Page speed affects everything about your website including page views, conversions, and SEO.
The faster your website is the more page views you have a chance to get. It's well known that a faster site will not only make your users happy, but allow them to surf more pages more quickly.
A faster site directly effects conversion rates. This has been tested and studied by many huge companies such as Amazon, MSN, and Google itself with the results showing:
"Even small changes in response times can have significant effects. Google found that moving from a 10-result page loading in 0.4 seconds to a 30-result page loading in 0.9 seconds decreased traffic and ad revenues by 20% (Linden 2006). When the home page of Google Maps was reduced from 100KB to 70-80KB, traffic went up 10% in the first week, and an additional 25% in the following three weeks (Farber 2006). Tests at Amazon revealed similar results: every 100 ms increase in load time of Amazon.com decreased sales by 1% (Kohavi and Longbotham 2007).
Experiments at Microsoft on Live Search showed that when search results pages were slowed by 1 second: (Kohavi 2007)
- Queries per user declined by 1.0%, and
- Ad clicks per user declined by 1.5%
After slowing the search results page by 2 seconds:
- Queries per user declined by 2.5%, and
- Ad clicks per user declined by 4.4%
Google has stated publicly that the speed of a page affects SEO. It's not a huge amount right now, but it could be the deciding factor between you and your competitors if everything else is the same. A fast load time is important in many factors for your website and it should be at the forefront of everything you do.