I'm basically summing up what the other two have said, for reassurance. The key phrase you used was "don't draw incredibly seriously, it's only for fun". As an artist, it if's just for the lulz, nothing you plan on selling or commissioning, then of course it's fine to pick up some reference photos for said things like body poses and such -that's why they are there :)
However, I feel it's more comfortable, if not justified, to use reference poses that are there for that very purpose. Studying references, and making some of your own, can help in the long run (like this deviantart gallery http://browse.deviantart.com/?qh=§ion=&global=1&q=poses). However, references are NOT meant to copy or try and replicate.
For example, I wanted to paint Aradia sipping tea. SO I looked up "sip tea" to find photos with a pose like that and got something like this: http://fav.me/d1s8rsx
I look at poses similar to that one to help inspire me to draw my own version, and the results are http://fav.me/d5xf41d
Reference photos good for: pose inspiration, practice, body study, etc
not good for: complete tracing, copying, uncredited use.
If you used a pose to the very lines, at least credit them if you plan to show off the work. As long as there's no profit or popularity involved, it's fine :D
Hope we all answered your question.Good luck! Have a good day too :)