Internet ad impressions grew by 14.7 percent in Q1, buoyed by search as the main driver and rich media, which gave display a boost, according to Nielsen Monitor-Plus. Again, while healthy, the numbers show significant slowing in online ad growth, as Nielsen said online grew 31.9 percent in its Q107 survey.

The new numbers come amid a flurry of data in recent days that also chart the online advertising slowdown this year. On Monday, the National Newspaper Association issued research showing that revenue slowed sharply in Q1 for newspaper sites, with revs rising only 7.2 percent compared to the 22 percent gains recorded the year before. Last week, TNS Media Intelligence reported that display ad dollars in Q1 came in with an 8.5 percent gain, reflecting a large gap between the 16.7 percent figure from the same period in 2007. More from Nielsen’s numbers here. Lots more details from Nielsen’s and Pubmatic’s reports after the jump.

While the differences between this year and last are mostly a result of the law of large numbers, the sputtering economy could be having some impact, according to figures from web publisher consultant Pubmatic. A number of industry observers have maintained that the larger economic woes would not significantly dent online ad spend. In an investor’s note issued on Monday, Doug Anmuth, Lehman Brothers internet analyst, endorsed that view again after his team conducted interviews with executives at WPP’s GroupM Interaction, Publicis Groupe’s Digitas and Aegis. That said, last month Anmuth revised his 2008 online ad spend outlook down a bit to 23 percent growth from his previous expectation of 24 percent gains.

As for Pubmatic’s view, its research showed that online ad prices were essentially flat, slipping 0.7 percent in May after the previous month’s precipitous 23 percent drop. Its second monthly PubMatic AdPrice Index is based on data from more than 3,500 publishers and billions of ad impressions. Looking at individual segments, entertainment, news and technology sites continued to fall, dropping by 11-, 13 -and 22 percent, respectively; sports was flat, while gaming and social net sites proved the exception—prices in those two categories rose 51 and 66 percent in May. Release

—Nielsen: Among online marketers, the health and telecom sectors posted strong increases in sponsored search link impressions, gaining 108 percent and 80 percent respectively. Hardware and electronics advertisers also saw robust growth 65 percent growth, followed by automotive and consumer goods companies, who posted increases of 45 percent and 42 percent respectively. On the down side, financial services companies, historically among the largest online advertisers, decreased investment during the period in both sponsored search impressions, which were down 15 percent as display fell 13 percent.

—Pubmatic: The gaming and social net gains the company saw in online ad prices pushed up sites with at least 100 million pageviews a month; those sites showed the biggest improvement compared to medium and small sites by rising 16 percent from April, growing from 18 cents to 21 cents. Medium websites were stable, while smaller sites saw prices drop 12 percent from the month before.

• Hard Times For Newspapers Gets Harder, As Q1 Online Ad Growth Stalls At 7.2 Percent Gains
• Display Ads Grew 8.5 Percent In Q1, Down From Last Year’s 16.7 Percent Gain: TNS
• Online Ad Spend To Gain 23 Percent In ‘08; Lehman’s Anmuth Revises Forecast Down Slightly
• 2007’s Online Ad Spend Grew 18.9 Percent, Down From 35 Percent The Year Before: Nielsen