Blowfish: hex digits of pi used for s-boxes?
Yes.  Blowfish's S-boxes serve a similar purpose as AES's S-box.

The P-array is used as part of the key schedule, to make sure that each round is different (this helps prevents slide attacks and related-key attacks).

I recommend you read the official specification of Blowfish and Wikipedia's article on Blowfish for more about the design rationale for Blowfish.

The use of digits of pi is a "nothing up my sleeve" number.

Bruce Schneier (the algorithm designer) wanted to use a random number.  For Blowfish, it basically doesn't matter what number you use, if it is random.  However, Bruce also wanted everyone to be able to see that he didn't somehow pick some very special choice of number that introduces a trapdoor.  The digits of pi are basically random-looking, and cannot be controlled by Bruce.  Therefore, they make a standard choice for a "nothing up my sleeve" number.

See also How to choose constants in a cryptographic function? and Wikipedia on nothing up my sleeve numbers.