I am not sure why.... but I have been getting some decent runs in on the treadmill at the Fitness Center.  I used to fight joining the fitness center all the time... but now that I am a member... I am so thankful.  Sometimes it really is nice to mix things up... I don't mind running on the treadmill watching the morning news sometimes....
Strangely enough... running on the treadmill makes me run a little faster outside.  I am not sure why that is, but it does.  The treadmill also gives me opportunity to do incline off and on and speed differences off and on and easily monitor it on the screen.  Its good training.
BESIDES the running aspect though.... (I mean what else is there besides that right?)  The gym is definitely a great place to get some cross training in!  So many options!!!