I've been following my DO allocation using New Relic. When I first signed up, I noticed the hypervisor stealing from my allocation. Not a lot, but some. After a week or two, however, this ceased. I can now report that for almost a year now I have been receiving my full allocation. I am very pleased with DO, but based on the good things that I've read on here, I'll give Linode a shot if DO ever drops the ball horrendously.

Where have you seen that you have a dedicated CPU core on Linode?

In the VPS market it's nothing unusual to oversell CPU, you can't only have 24 VM on a single server, that doesn't work financially (except if they count threads from hyper-threading as a core but that's not dedicated).