I have been slow rolled. Some of the people just do it intentionally as a form of mind game. Some do it unintentionally. I don't let it bother me so much because there are time that I also misread hands and might take time to find my way to process the action. If slow rolling on a poker table is done with malicious intent, it is pure unsportsmanlike and should be frowned at entirely.
Nothing create unexpected tension in poker room like slow rolling. I have been slow rolled in home games uncountable times but I don't find it offensive because I don't have much to lose. Slow rolling is part of the game but it must be done with caution and respect.
There is a time and place for a good slowroll just pick your spots carefully. i like slowrolling friends instead of strangers, its more of a respect thing really. i only slowroll the river with the nuts when i do, slowroll flop or turn and the 2 outer will get there more often, karma and the poker gods will teach you a lesson!!!