Chances are, your slides look like crap.
It shouldn't be that way. The presentation you give is undermined by your decision to use that cutesy 10-point serif. Luckily, you don't need a lot of design chops to improve the way you present yourself.
From the conferences I've gone to, certainly a number of people "get" it. Great slides, very readable, pleasant to stare at for 50 minutes. But those presenters are in the distinct minority.
We want to live in an idealized world where the content of your talk is what people pay attention to. But that's far from reality. People base their opinion of your talk, in part, on your slides. Maybe it's unpleasant to think about, but pleasantries don't dictate realities.
It's hard for me to remember a terrible presentation with a great set of slides. It's hard for me to remember a great presentation with a terrible set of slides. Good speakers pay attention to everything: how their slides look, how they speak, how their content comes across.
It may sound like you need a fabulous slide deck to make an impact. You don't. I've been in plenty of presentations where I suspected the speaker was uncomfortable with their design talents, so they instead opted for simple, huge text on white or black backgrounds for every slide. That's great. Those very basic concepts — huge, readable, minimal text — will immediately push you ahead of 90% of everyone else. No joke.
On-screen code is incredibly important, too. There's something about putting code samples on-screen that leads decent presenters to just say Oh fuck it! That's fine! Code samples are a fragile move in the first place, since they require a more intensive cognitive process on the audience's part to understand what's going on. On top of that, syntax highlighting makes it hard to read. A speaker at the last conference I went to had 20 lines of code on one slide, with black-on-grey text (except for the line he was talking about, which was white-on-grey). It's insane.
Put yourself in your audience's shoes. Think about how the design of your slides augments your talk, rather than detracts from it.
Developers aren't "supposed" to design, I know. And it's a very personal thing: some people are more artistically inclined than others, and I'm not expecting every developer to be able to pass some university art school program. What I am saying is that design is important, and you should care about how you present yourself. Designers can get by with fancy, intricate designs, but you'd be surprised at how easy and powerful a simple, no-frills approach can be.