dude, you couldve just asked two questions in the same thread.

anyway, do a search for "tires". there are many different opinions on this. i do this for a living and i would NEVER suggest riding on two different to my customers for many reasons. i dont feel like going into depth, but the main reasons are
1) different handling/comfort/riding characteristics
2) different sidewall strenths
3) different treadwear
4) looks retarded
the ONLY time i would ever run two different brands or even model tires if if i absolutly had to. for example, i have $120 in my checking account, dont get paid for another 2 weeks, and just had a blowout.