I'm pretty sure I had more trouble than most with my CK30, look for posts I've started for all the details. While I don't think my experience was normal, I do think there is a bit of an issue with the HST in the CK line. For whatever reason, they can develop a bit of a forward creep and the rocker pedal doesn't re-center itself. My dealer went to the extreme of replacing the HST as he said he'd had a few tractors like that and replacing the HST was the only way to fix it. After it was done, the problem was fixed. A lot of people here think it's just adjustments that need to be made, but I don't remember anybody else saying they fixed the issue, only improved it. You'll find plenty of threads on the topic in the Bobcat section as well (CT225 = CK27, CT230 = CK30, CT235 = CK35), even a service bulletin from Bobcat that somebody posted.
They're great tractors and I don't think the HST is prone to failure, but the creep is a little annoying and can be dangerous if you're doing work in tight spaces. You get very used to re-centering the pedal manually which stops the tractor and it stays where it's supposed to. After all the issues I had with my CK30, I traded up to a DK45, I believe I got a bit of a lemon the first time and I really do think they are great tractors and are build like brick **** houses.