Everyone loves the idea of a robot that cleans for you. But not everyone is enamored with iRobot's ( IRBT) vacuums -- or its recent stock performance. iRobot is the Massachusetts-based robotics company that leveraged 20 years of expertise in military robots to produce Roomba, the first self-guided vacuum priced below $500. The company has sold a million-and-a-half home robots since 2002, marking a strong entrée into the consumer market that paved the way for one of the most successful IPOs last year. But 2006 is proving a mixed year for the Roomba. As of Friday, the best-selling Roomba on Amazon.com -- the Roomba Red, which at $150 is the lowest-priced model the company sells -- stood at No. 47 in Amazon's kitchen and housewares sales rankings. Other vacuums ranked higher, including a Eureka Boss Smart-Vac in fifth place and a Black & Decker ( BDK) DustBuster at No. 10. Both of those better-selling vacuums also carried higher ratings from Amazon customers than the Roomba did, garnering four-and-a-half out of five stars, compared with Roomba's four stars. Four out of five isn't bad, but among Amazon's 50 best-selling housewares items, only two had fewer than four stars. Other models, such as the $249 Roomba Discovery, were rated three-and-a-half stars. Most of the user ratings on Amazon, as well as those on other review sites like Cnet.com, are positive, with such comments as "I love my Roomba" and "This vacuum is a life-saver." One recent reviewer proclaimed, "This has become a part of our family and we have named her Ruthie." But some of the neutral and negative reviews display a vulnerability of the Roomba: Many consumers expect more from a robotic vacuum cleaner than they do from a traditional vacuum. And when Roomba shows quirks and even weaknesses that other vacuums don't, people will speak up.