I keg and force carbonate, and my beer has really fine bubbles. Is there something that I can do (turn up the pressure, maybe) that will give me larger, coarser bubbles in the finished beer? Thanks!
Really, fine bubbles is usually what people are after. Are you hoping larger bubbles will cure a different problem like head formation or retention? This type of information might get you an answer more suited for what you need. Bubble size is a tough thing to control and quantitate. It involves the size of the nucleation sites and the amount of insolubles in the beer. Its something the pros really struggle with too, and its something that brewing scientists still pore over in research settings.
In short if you want bigger bubbles, you need cleaner beer and cleaner glassware. And more pressure will give you just more bubbles of the same nature.
When you say bubbles, do you mean the mobile bubbles that form near the bottom of the glass and migrate upward, or do you mean the cells in the foamy head that collects at the surface?
My understanding of actual bubbles is essentially what brewchez said above: it's a function of glassware and suspended particles in the beer.
Head retention however is a different topic, and if that's what you're asking you might re-ask your question in terms of head density, head retention, head texture, etc.