I can only speak for my experience with an iPad, but as an example theres no way of saving documents easily so when you hit the "browse" button to upload your CV to an application site you would have no where to go. The vast majority of jobs I've ever applied for all need CV's to be in .doc or .docx format so you need to be able to edit / save / upload these on the go. Even just simply things like not having a full keyboard make it more of a faff on a tablet. This is before you get into the more specific issues like how utterly appaling some companies website are when it comes to handling different borwsers, let alone the mobile browsers on tablets.
The situation might be better on Android, but I would just want to avoid the situation of coming across the perfect job that you cant apply for as the website only works in IE. With that in mind I'd never consider going for anything but a laptop. If you were just travelling I'd say a tablet, but its the handling CV's / applications side of it that means you really need Windows, Internet Explorer, and an Office suite.
Unfortunately I can't link to the type of laptop I would suggest as Overclockers dont stock any below the £700 mark and I cant link to competitors. Something like the Asus X200CA would be my choice. 11.6" screen, dual core celeron, 4GB of RAM and 500Gb HDD should be plenty powerful enough.