I do it, and I spend part of each session furthering my power's goals, the rest of the time I'm trying out other stuff - I spend a lot of my time trading rares in an ASP for example, but I'm gradually working through the other ways of playing, this week I tried mining for a while.
It seems to me that the people in this thread fall into two groups - those who do play it, and consider it a useful extra, and those who haven't played it but see no reason to let that colour their opinion about it being rubbish.
PP is like a big game of Risk, there are several actions (these vary a bit from power to power) that you take to earn points, these points are used to advance your own rank within your power (with increasing rank come increasing rewards, up to 50m credits a week pay packet for the maniacs with no life, whilst a 5m cr weekly pay packet is doable although does take a good few hours to run off). The points also advance the cause of your power, allowing you to defend systems against enemies or push into and capture theirs.
Some of those missions involve running between allied bases carrying packets - this might be referred to as intel, or supplies, but basically amounts to small loads of cargo that get eked out every half hour. Other missions will involve going to enemy systems and shooting their ships up, or going into combat zones and having a good scrap. Most normal players will, I imagine, do it the way I do - run a few missions to rack up some points, then go off and trade or whatever as per the normal game to earn credits, upgrade ships, explore, and so on - PP is kind of like a side game you drop in and out of at will when you fancy a bit of a change.
The reddits (see links at page top) and the discussion threads here should suffice to show you that a fair amount of thought goes into each 'team's' planning each week to try to optimise their approach to the current setup - get it right and your power climbs the greasy pole, mess up and you drop. To complicate matters many people seem oblivious of the forum, and go off doing their own mission stuff without having a clue that there's actually an organised group on the forum trying to coordinate things to best advantage....
Bad side to it all? Well, it IS hard to find out exactly how to do everything, the 'instructions' on this stuff are useless and woefully incomplete. You also find that the powerplay info in game (you know, down with the tabs for system and galaxy maps) doesn't gel with what you see on the reddits, which is where you really need to look for the thinking player's guide to which systems to by flying around doing whatever I.
As for the 'grind' - to quickly, and fairly accurately, summarise - whatever you earn in one week, you carry half those points forward as a starting amount the next week - I earned just over 1000 pts last week, this week I had 500 banked before I started playing. This helps you rank up of course. Also, as you rank up, those small parcels of cargo that get you points increase in size so you hang around less filling your cargo hold....everything accelerates so that although the rank grind DOES involve steadily increasing totals to achieve the next rank, the reward system makes it less painful than it might first appear.
Final tip - if you go for it, check the powerplay map display and pledge to a power from within that power's space - like an idiot I joined my power whilst sitting inside an enemy power's space, and got killed twice trying to 'get home'!
Dave