I belong to a very traditional Presbyterian Church, and wear a tartan kilt every chance I get. It is always very well received, especially by the women, and every comment I hear from the guys is positive. The minister, who has studied in Scotland, takes the position that it is very appropriate. I always wear a white, dress shirt and tie that compliments the particular tartan. Unfortunately, I don't yet own a casual jacket, only a PC, which is much too formal for daytime worship services IMHO.