I have leveled an alt to 58 recently and have only been ganked like 4 times the entire leveling run (though my class is a Rogue...) So I'd really have to ask, is leveling on a PVP server with the newly added CRZ really that bad? I've heard tons of complaints about Cross Realm Ganking from people on various forums (though they only got the "PVP is PVP deal with it, loser" response).
It can be. Sometimes an entire zone will be camped for hours and no level 90's can help you. The main reason people complain is because most gankers specifically target low levels and refuse to fight any level 90 players. Some will go night elf druid. Gank, go stealth, fly away. Some go rogue for vanish + cloak and go about killing low levels all day. Forget leveling in the zone the dark portal is located. Depending on the time, youll die as soon as you zone into it.
In short, it can be. Just depends on what time it is and if anyone is around who wants to kill low levels. Most of the time though, getting a level 90 buddy wont do ya any good. They will just gank and run. Or gank / let themselves be killed. They don't care. As long as they get to kill ya.
When I have some spare time I fly to hellfire and help people with 90 gankers, go figure
Some rogue killed quest giver east of HH for hours, I just spammed clicked charge+mortal strike near the quest giver and got him a few times, but geez...