ClickZ reports that research by the Interactive Advertising Bureau (IAB) and PricewaterhouseCoopers reveals a decline in the growth rate of online advertising expenditure.

In the first half of 2008, $11.5 billion was spent on online ads. While this constitutes an increase of over 15 percent over the same period in 2007, it’s much lower than the 37 percent increase in the first half of 2006 compared with 2005.

Also, while online ad spending in the second quarter of 2008 was 13 percent the second quarter of 2007, it was 0.3 percent lower than what it was in the first quarter of this year. In other words, online ad growth looks to be dipping.

Nevertheless, online spending was still significant in the first half of the year. Search engine ad spending (about 44 percent of all online ad spending) grew to $5.1 billion, up 24 percent over the initial half of 2007, while display spending (33 percent of all online ad spending) rose by 19 percent to $3.8 billion in the first half of this year.

Most display spending was devoted to banner ads (21 percent). The remainder was devoted to rich media (7 percent), video (3 percent) and sponsorships (2 percent). Meanwhile, spending on online classifieds decreased from 17 percent to 14 percent in the first half of the year and lead generation ad spending dropped from 8 percent to 7 percent of budgets. Email remained steady at 2 percent of online ad spending.

Finally, advertisers continue to embrace performance-based ad models. Performance-based ads, such as cost-per-click or cost-per-acquisition ads were up for 52 percent of ad spending in the first six months of this year, up from 50 percent in the first half of 2007. Meanwhile, CPM-based ad spending dropped slightly from 45 percent to 44 percent.

Source: Kate Kaye, “Online Ad Growth Declines in First Half 2008″, The ClickZ Network, October 7, 2008

An AOL-sponsored study by Beta Research Corporation has just confirmed what we probably all thought (based on our own habits): THERE IS NO ONE TIME that most people check their email. U.S. Internet users check their personal email throughout the day, including at work.

The June 2008 survey found that while nearly one-quarter of Internet users were most likely to check their email upon waking, more than one-third checked throughout the day, and the remainder checked at various times, including during the night. Over 70 percent of employees checked their personal email at work, and nearly one-third checked more than three times a day.

For email marketers, the implication is clear: trying to time your email delivery to the hour may be futile. Your target market is mostly likely to check their email several times per day, and while they may not see your email when you send it, they are likely to do so later on.

Source: eMarketer, “When Do You Check Your E-Mail?” eMarketer, August 8, 2008

According to the “Q2 Bellwether” report, released on Tuesday by the U.K. based Institute of Practitioners in Advertising (IPA) and Market Economics, growth in U.K. online ad spending grew just 6 percent over the first quarter of 2008.

This is the slackest rate of growth since 2003, and much lower than the 21 percent growth in the previous quarter.

Tougher economic conditions seem to be taking their toll on U.K. Internet marketing expenditure. Of the 250 companies surveyed for the report, only 19 percent increased their online budgets during the second quarter, compared with 27 percent in Q1. Furthermore, 12 percent decreased their budgets in Q2, compared with just 5 percent in the preceding quarter.

Online ad spending is expected to remain constrained throughout the remainder of the year.

Source: Jack Marshall, “U.K. Online Ad Spending Slows”, The Clickz Network, July 15, 2008