Clever. "the warmest year of the twentieth century" is completely true. But it seems a little misleading, since there's been a few years even warmer in the 21st century.
Whenever I see the year 1998 mentioned in a discussion about climate, I am immediately suspicious. The temperature recorded in 1998 was a serious outlier.
Let's pretend the datapoint from 1998 did not exist. Then we could accurately say, "The last decade has been hotter than any previous year on record!". But with 1998, you could accurately say, "Most of the last decade has been cooler than it was in 1998!"
It's always nice to look directly at the data. http://data.giss.nasa.gov/gistemp/graphs_v3/Fig.A.gif
It's true, if you take the past 10 years only, the trend is pretty flat. But if you look at a 10 year running average we're in the middle of an upslope. We can even make it look like we're in a cooling period if we pick 1998 as the first year! Fun with data.