Separate reports published this week quantify the impressions of many Internet buyers this shopping season: e-commerce sites are slowing down or not working at all.

Beginning the week of Thanksgiving, when average download time was 4.81 seconds, performance has degraded 16 percent, to its current time of 5.74 seconds, according to Service Metrics.

Meanwhile, Andersen Consulting yesterday went public with a study indicating that more than a quarter of the purchase transactions at online stores never go through.

Chicago-based Andersen said of the 100 top online stores, it was only able to complete 350 purchases out of a total 480 attempts. Andersen Consulting also noted that "pure play" electronic retailers generally performed better than the online outlets of traditional merchants.

Service Metrics today released its TurboSanta holiday performance results for the week of Dec. 13-19. Performance scores for the TurboSanta index degraded for the period to 5.74 seconds, down from 5.65 seconds the previous week.

The worst of the shopping crunch is over, said Service Metrics' spokesman Bill Quinn. But while he anticipates the declining traffic volumes to result in improving performance, online consumers who have had difficulty placing orders may not be back.

Both the fastest and slowest online sites slowed down this week, according to the TurboSanta index. The 10 top-performing sites ranged from 0.54 seconds to 1.86 seconds, with an average download time of 1.41 seconds this week, down from 1.38 seconds the prior week. Similarly, the 10 slowest sites in the TurboSanta index worsened to an average of 21.74 seconds this week, down from 19.32 seconds last week.

TurboSanta continuously monitors the 120 top retail sites, including the top 100 e-tailers as rated by the National Retail Federation (NRF), and divides those 120 sites into 13 vertical market categories. Performance data is updated to the Web site hourly.

Unhappiness with the shopping experience at different online stores could have a lasting impact on some e-tailers, according to some observers. "I think shoppers will be less forgiving than last Christmas," Quinn predicted.