You should never use a work computer for anything personal from banking to even reading wikipedia. Its just dumb.
My philosophy: if the hardware doesn't belong to me I'm not doing anything personal on it, no exceptions.
True, if you work for very early startups with no IT department, life is a lot more free. Just be careful when they grow to the point of having that IT department.
Also be aware of peer comment, devices can be shipped direct from manufacturer but already pre-registered to be company-managed. But this does require said IT department to exist to be managing this.
I do make exception to my hard rule on not sharing company/personal activities on devices when working with tiny startups where this is not an issue.