What I have observed of people moving to part time (even mostly full-time as you suggest) is that they are taken less seriously and are seen as less committed. This may translate into getting less interesting projects because they see you as having no promotion potential. The fewer hours worked, the less seriously you are taken. So working 80% of the time would have a lower impact on the quality of your assignments than half time, but I would still expect some unless you are the only person qualified to do the work which is another whole issue.
You will definitely miss some meetings (hey that could be a blessing!) because people will schedule them on your day off. You might come in on Monday to find that you have been assigned to some less than desirable tasks because you weren't at the meeting to defend yourself.
As to being called in on your day off, I would expect it to happen about as often as you are currently called in on a weekend. If you move from salaried to non-salaried in the move, you might get called in less than you do now because they would have to pay you. (I've certainly observed this the other way in moving from non-salaried to salaried and suddenly my overtime hours tripling.)
You might also be the recipient of some resentment from peers if no one else is allowed to move to part time (especially if others have been turned down in the past). You could be viewed as receiving special treatment. This is going to vary wildly depending on the particular colleagues you have and the reason you are moving to part time.
We have one colleague who recently went part time as he is getting ready to retire in a couple of years and he works on a client that the rest of us have no responsibility for and I have have seen no resentment. On the other hand I had a friend who could only work part time due to chronic fatigue and her co-workers gave her hell for years until she retired because they didn't believe chronic fatigue was a real disease. It also took her out of the pool of people available for out-of-town assignments making the rest have to be gone more frequently which didn't help the resentment.
A woman going part-time to care for children might face a lot of resentment from a mostly male workforce or from older women who didn't have that option when their children were young. Someone going part time to do chemotherapy on the days off would likely be given alot of support from co-workers. So the reasons can make a difference.
The best thing to do to make a move like this successful is to communicate. Try to make sure that they know how to find information they might need on your day off. You should have someone else available who knows where your stuff is and can look it up and answer questions. Remind people you won't be in until Monday when deadlines are getting close and ask them, on Thursday morning (or Wednesday night on a big critical project), what they might need from you before you leave.
Depending on why you are off (clearly not if you are having chemotherapy and feel sick), you might consider checking your emails a couple of times that day to see if anything critical is happening. Or provide your boss with a cell phone number to call in an emergency (if you can trust him to only call in a real emergency).
Try not to leave things hanging on Thursday that can be finished quickly. If you put in that extra half hour on Thursday so something doesn't sit until Monday, people will view you more favorably.
Be more aware of deadlines and how your work might impact others. For instance if you contribute to something that is going to need to be sent out on Monday, don't leave your part of the project until Monday when you get in or people will be stressing that you will not get done in time or not give them time to review your part if need be. This is particularly true if you have unmovable deadlines like those to submit project bids or to respond to regulatory requirements. The more you make sure your absence doesn't cause them problems, the more likely they are to start giving you better assignments as time goes by.