I'm seriously considering purchasing an iPad in part for job interviews and for client meetings... my thinking is that it is much less cumbersome than pulling out a laptop, it shows that you are somewhat tech-savy, and its size allows you to keep it with you at all times (you never know who you might run into that will want to see your work!) Still debating about whether it's worth the price, though...

One of the reasons I bought an iPad was to showcase my work for clients instead of bringing printed pieces. Of course I'm goign to do some leave behind piece but I realized I could spend $330 for an iPad Mini and it would be cheaper (in the end) than printing out pieces AND going through aggravation of reprints. And like Lila said, it shows you are tech savvy, which I am seeing is a huge plus. 

As someone who interviews a lot of design candidates, I think an iPad is acceptable for showing interactive work, especially if you can use it to demo/show live sites or apps.

If you are showing screen shots in a portfolio-style app/site, it is not as good since the interviewer cannot see enough details. On an iPad mini, this is even more of an issue, All in all, I think a laptop works better since the screen is larger.

Also, while you may want to include images of print work in an online/on-screen portfolio, if you are interviewing for a role that includes print design, I'd recommend bringing print pieces with you so an interviewer can see them firsthand.