If you read
PostSecret and you wonder about this week's moose from Maine, I've deciphered it. (I guess being anonymous is not enough for some people.)
It's a simple shift/transposition cipher. There were a couple of errors in the encryption. Treating an uppercase "I" as a lowercase "l" (that's "i" and "L", in case your font's as helpful as mine) fixed one; and the other was forgetting to transpose a letter from the cleartext, making "thil" "this".
Pt avv zjhylk av zhf
P SVCl fvb iljhbzl
P ruvd zvvuly
vy shaly P dpss
il aol vul av mbjr aops
bw.
Pt zvyyf.Im too scared to say
I LOVe you because
I know sooner
or later I will
be the one to fuck thil
up.
Im sorry.
For those with Unix,
tr a-zA-Z t-za-sT-ZA-S