Getting tired of screen font Verdana, blog designers tend to switch to typeface Tahoma which is essentially Verdana condensed horizontally. Verdana’s great readability at text sizes is partly due to the space within the characters, but this gives it a long line length. You can fit more text in the same space with Tahoma, which is helpful for dialog boxes.

Here is a screenshot of Verdana compared to Tahoma.

(Textexample was taken from Daniel Woods blog tinear.net)

Obviously Verdana´s natural tracking (kerning) is much more balanced than Tahoma´s is. F. e. compare the word electricity.

Tahoma in standard format is far not that smart as Verdana is, at least not without an appropriate kerning. If Tahoma is chosen for long write ups, apply correct line-height and letter-spacing.
Here is an example.