According to the results of consumer surveys done by the American Consumers Union, Dyson is a relatively reliable brand of vacuum cleaner. Here is a quote from the preamble to their "Vacuum Brand Reliability" Webpage:
"Kirby was among the least repair-prone brands of upright vacuums while Simplicity and Riccar were among the more repair-prone. Among canister brands, Dyson and Kenmore were among the least repair-prone and Electrolux was most repair-prone. That's what we found when we asked almost 96,000 readers who bought a vacuum between 2007 and 2011 about their experiences. The graph shows the percentage of models for each brand that were repaired or had a serious problem. Differences of less than 4 points aren't meaningful, and we've adjusted the data to eliminate differences linked solely to age and usage. Models within a brand may vary, and design or manufacture changes might affect future reliability. Still, choosing a brand with a good repair history can improve your odds of getting a reliable model."
For uprights, Dyson is in the top five for brand reliability (Kirby 3%, Kenmore 6%, Dirt Devil 6%, Dyson 7%, Bissel 7%), and for canisters, Dyson is right up there with Rainbow (Rainbow 6%, Dyson 8%, Kenmore 8%, Miele 11%).