I like to write all my GM posts in present tense. I also like to use second person as much as possible when referring to the player characters. Consider:

"She smelled the ogre's lingering body odor." 

Or:

"You smell the ogre's lingering body odor."

I think it helps make the scene more immediate and immersive. This can get tricky when you have several different characters who would notice different things, like if you have one character who can see in the dark. For this I have a color system to help delineate which descriptions only your character would notice. I assign each character a color, and will then color the description.

Character: [color=8585AD]Infrared Dude[/color]

[quote] 
Cold air breezes through the passageway as you creep through the shadows. [color=8585AD]Just ahead, a figure emerges from around the corner, exposed face and hands haloed in a rainbow corona of emanating heat.[/color] The sounds of padded feet on stone echo in the dark. 
[/quote]

As a player, however, I write exclusively in past tense, third person, using first person in inner monologues.