Depends on whether you know a bored or up-and-coming trademark lawyer who's willing to defend you against the inevitable lawsuit. Companies with trademarks
have to defend them aggressively, or they can lose the right to enforce them at all. So even if they don't actually object to google-my-shmoogle.com, they may launch a suit to get the issue in front of a judge who can say whether that's infringing or not. If they don't, a genuine infringer like gooogle.com may point to g-m-s and say 'well you didn't sue them, so you've effectively abandoned your trademark and now it's free for the taking.' Unlike copyright, trademarks can last indefinitely; but also unlike copyright, if abandoned or left undefended there is no automatic or minimum period of legal protection. Also, the usual copyright arguments like fair use or parody do not apply to trademarks in the same way.
As long as you are not competing in the same market and there is little or no risk that consumers will confuse your brand with that of the famous brand, derivative brands like this will often be allowed to stand. The point of the big brand owner has been made, the big brand has been defended at law, and can be defended in future against attempts at infringement. With the examples you provide, I'd suggest a 50-50 chance of success for the first one but only a 5% chance of success for the second. There's no hard and fast rule; trademark litigation can get very hand-wavey. It has to be said that some companies launch and then switch to a plan B name...after they've accrued a bunch of free publicity by incorporating the famous brand and declaring themselves to be shocked - shocked - at the subsequent legal action. It's a nice reliable David-and-Goliath story, especially effective if the David company is some little cottage industry focused on kids/kittens/kitsch.
I'm not a lawyer, and certainly not a trademark lawyer, so don't treat this as legal advice.
