Noun project is great for wireframes.

Use stock / sets as placeholders & for initial feel, then do a discrete phase where icons are redone by hand in whatever fashion compliments the overall art direction.

Depends on the stage of the product. When I've worked on launching new products I tend to use icon sets, as in these situations we want to get something out the door quickly and being the only designer found that I would rather spend my time focusing on getting flows and general creative direction down than spending hours on nailing that perfect icon. When working on a more established product I feel like I have the time to actually sit down and make my own custom icons. Regardless though, even when using an icon set there's usually always going to be a unique action which requires a custom icon.

I actually do both. I have created icon sets for myself over time and sometimes reuse them for generic uses. But I try to make each project unique if possible and create new icons for heavy use areas.

I would suggest making icon sets as I do. It helps to train yourself and also gives you a free set to work with. Not to mention feeling great about knowing you created everything.

So far I've used icons sets...supplemented with the occasional custom one to fill a need here and there. I'd love to have a project with a branding need for custom icons and a corresponding budget to permit it. For the most part though there are plenty of existing icon sets that work for most smaller projects.

Depends if they're paying for them or not. If there's not a budget I evaluate it on a case by case basis.

Also there are lots of really great stock icon sets out there for cheap. You can also have in-house teams do icons and art direct them if you're working with a bigger client.

Spending time to make good unique icons isn't easy so it's nice if you're handling the UI to have someone else who knows the brand focusing on that part.

I go custom 90% of the time, but use icon sets for a lot of my inspiration. If you're trying to build a brand with a distinct visual style I think it's important to own your icons, if you aren't icon sets are super valuable and well worth the money.

Custom. Always.

I'm not against icon sets, but I like drawing icons, and we typically have needs that may not be well met by icon sets.

I'm not the type to use other people's work, even if it's free, but Entypo is just so convenient and looks great. I'm using it on my latest project. http://entypo.com

At first I start with icons from icon sets, at the end of a project I make my own versions or sets. Well.. sometimes when I'm really lazy I just use the sets.