Property web site operator Rightmove found the market hard to please on Wednesday, as the growth in page views on the site slowed down in the first quarter of 2011.Page views on the Rightmove.co.uk website during the first three months were up by around 15% on the same period a year ago, and on many occasions single day traffic levels have been higher than any seen in 2010. However, the year on year growth rate is down from the 17% improvement seen in 2010.Searches on mobile devices were over 200% higher in the first three months of 2011 compared to the same period a year ago.The site's market share among property web sites remained steady at 2010's level of 82%. Rightmove agency membership at the end of March stood at 14,864, up slightly on the end of 2010. The overall number of advertisers at the end of March was up 0.7% from end-December levels, and growth has continued in April. The growth has come from modest increases in the number of lettings only agents and new homes developments. Average revenue per advertiser "increased substantially", Rightmove said, without releasing any figures, though the company did indicate that it is line with the company's aspiration of achieving an increase to around £439 per month in 2011, compared to £379 per month in 2010.Operating costs remain low and are unlikely to exceed the £29m indicated at the full year results in February, and subject to there being no further decline in the UK housing market, the board remains confident of meeting its expectations for the full year.---jh