Unsurprisingly, dramatic mobile search ad spending growth continued in the US, with year-over-year growth in Q1 up an astonishing 221%. The ongoing popularity of tablets has clearly captured the attention of advertisers, who spent 67% of the total mobile search ad budget on the devices in Q1.

Ad clickthrough rates, however, were slightly higher on mobile phones with full browsers than on either tablets or PCs.

Travel had a breakout quarter for search advertising, with marketers increasing their global search ad budgets in the sector by 59% year over year in Q1. According to IgnitionOne, the travel search advertising growth rate outpaced that of the retail sector, with travel also seeing increases in both impressions and clickthrough rates.

News was good for the Yahoo!/Bing search partnership, which snagged a 21% market share in Q1, the highest since the two companies brokered their search deal in Q3 2009. The survey found that US search advertising on the engine climbed 46% year over year in Q1. Yahoo!/Bing also shrugged off the normal drop off in search spending that follows the holiday season, instead experiencing a 14% increase in quarter-over-quarter spending. IgnitionOne credited Yahoo!/Bing’s banner quarter to changes in its search engine that resulted in increased competition during ad auctions.

eMarketer estimates search ad spending in the US will reach $19.51 billion this year, up 27% over 2011. Search will garner 49% of all online ad spending in the country and 49% of mobile dollars as well.