Adam Jones has homered on 26.9% of the balls he's put in the air, but several other hitters have seen similar lifts in their home-run-per-fly-ball rates. HR/FB rate is a volatile stat, one influenced by several factors (such as home ballpark), and it can bounce around over a season. In general the average player hits about 10% of his fly balls for home runs, with the league leaders usually in the 25% to 30% range. Since 2002, the first year with complete data, the overall leaders are Ryan Howard (28.7%), Jim Thome (27.6%) and Barry Bonds (25.1%).
A look at the 2012 HR/FB leaders (data from fangraphs.com) shows that they're all outperforming their career rates. All are likely to see their long-ball paces slow as the year goes on—but they're also well on their way to healthy end-of-season home run totals.
Dodgers (page 46)
2012 HR: 12
2012 HR/FB: 41.4%
PRE-2012 HR/FB: 15.9%