In reply to Bobling: Hi, its not so bad at the moment really. In the summer the longer grass is normally more of an issue than the wet underfoot.
From Okey there are loads of options using the military tracks which are good to walk no matter how wet it is. To the West side there are also former tram/trackways especially heading away from Sourton which you can use to sneek past the wet and get out as far as the Rattlebrook (Bleak House, Kitty Tor etc etc).
It is a bit squelchy to the East side of the moor although the track which gets to Gartaven Ford from Buttern (edge of the moor from Throwleigh) is OK and gets you past the worst of it (Steer clear of the various "pools" and "mires"!).
The stream heights do rise but also fall extremely quickly. Have a look at the graphs shown on the Environment Agency Devon River levels website. Only a few hours after the rain has gone the upper streams drop to near normal. Do take care though.
I would use the military tracks to get out past Hangingstone Hill then wander about from there (do check the range isnt operating!!).
Have fun, its a beautiful place even in the rain!!