Well, Since I have been on PMC, for about a while, i can safely and confidently tell you that the forums give you No exp! So for all your people posting thinking that it gives you EXP, it doesn't! Blogs, Skins,Texture Packs,Projects and Mods give you experience. However, Texture Packs and Skins are seen more as they are more commonly wanted by the community. (That's why so many good skins are overlooked as many underachieved skins are being put in there place)

Table of EXP-
Diamond - 5exp
Favorite - NOT SURE (as i haven't had many favorite :P )
Comment - 1exp
View - 1exp

^
is a table showing you how much a certain thing gives you, such as a diamond, which gives you 5exp to a comment which gives a 1exp.

However I urge to community to look at other tabs, such as Mods, otherwise you will not be able to see any hidden glories, as you have not seen that tab. Also Spamming is not acceptable I saw a thread earlier with 'dddddd' as the title and spam words, I wrote that it should be taken down, as this person clearly DID NOT read the rules.

Overall, looking at a Blog such as this one, Or even a skin, can give someone 1exp higher, which is a nice feeling to get knowing that someone actually reads/looks at the things you post.