I don't own one nor have I used it but going by the spec sheet:
http://www.gsmarena.com/compare.php3?idPhone1=5071&idPhone2=5084 it seems to be a lot lighter than the iPad4. As for whether it gets warm, having owned a Galaxy Tab10.1 I'd say it probably does, all my Samsungs (Galaxy S2, Galaxy S3, Galaxy Tab10.1) tend to get very warm when used heavily, and so does my iPad, it's what thse gadgets generally do due to their ridiculously fast Multi core CPUs and GPUs, but chances are the Nexus 10 is probably more ergonomically friendly due to its rounded edges and plastic build, so it will be easier to hold and use for longer periods than the iPad4. - This is all based on assumption coming from my experience with other Samsung products.