• by Mark Walsh  @markfwal, November 29, 2011

Cyber Monday proved too much of a good thing for some retailers. The Web site of PC Mall was down for nearly an hour and a half between midnight and 5 pm EST Monday, making it the worst performing site among the top 50 Internet retailers, according to findings from Catchpoint Systems. It was followed by electronics retailer Newegg, with an hour of downtime, and Toys “R” Us, at a half hour.

Assuming Cyber Monday sales are spread evenly throughout a 24-hour day, an hour of downtime would translate to 4% of sales lost if buyers leave a retailer’s site out of frustration. A crash during peak times could mean even greater revenue loss, according to Web performance monitoring service Catchpoint.

The fastest retail sites based on render start time (the time it takes for a page to start displaying something other than white space) were Macys, Staples and Kohl’s. The slowest was Crate and Barrel. IBM's Coremetrics reported today that online sales were up an estimated 18% over last year on Cyber Monday.