Managers always put emphasis on R&D and technical competence. Normally, employees are expected to do R&D and personal projects for skill enhancement purposes outside office hours and preferably, in home. What if some employee got unexpected free time during his/her office hours, and instead of wasting time browsing social networking or other sites , h/she does R&D and to bolster skills, do some personal project. Unless warned or formally reprimanded, will this be considered as a violation of workplace ethic, given their engagement in activities which are more personal in nature than official? Or is it prudent or appreciable, in a sense that instead of wasting time browsing sites, employee is investing time in a productive manner to stay sharp to be able to contribute to the company in future?
Short answer, ask your boss. If you aren't comfortable asking then you probably shouldn't be doing it!
Longer answer, see below:
I don't think that "Workplace Ethic" is the correct term, you need to consider the company policy regards such matters.
This will vary from company to company and it should be documented if not you need to ask your manager.
If the "bolstering skills" is going to benefit the company by making you better at your job, then it's quite likely they will support you and be happy for you to do this activity at work as long as your work does not suffer. If you are researching to set up a company to compete with your current employer, they may not be so happy to put it mildly!
Is you boss aware of this unexpected free time? If they're not then maybe you need to let them know so they can assign you extra work or get you to help your colleagues who may be struggling with their work loads.
Whilst doing your own thing in your own time may seem to be reasonable and even ethical, you are using company equipment so they have every right to prevent you from doings things they don't like!
Regards your edit, do they need to warn you:
No they don't - if what you are doing is considered "Gross Misconduct" then they can sack you on the spot for it, but most reasonable companies would give some kind of warning if what you are doing isn't excessive or unreasonable! Make sure you are familiar with all company policies and check with your boss. The problem is that your definition of what is reasonable/excessive may differ from the company's definition so you should ask to get clarification.
If you are going to do anything that's related to your own personal projects, pick an activity, say within R&D, that you can justify to the company in terms of the salary they pay you.
If you can justify your activity exclusively in terms of the company's self-interest e.g. I am on Stack Overflow because I am looking for a more sclable algorithm to accomplish a particular task or I am looking for a more theoretical understanding of what I am doing so that I can make my implementation more effective, then t's likely that your company will not query you very hard.
I'd stay away from mentioning doing anything personal on company time. At best, the management ignores what you just said or queries you mildly on it. At worst, they run an inquisition on you and put you through the wringer. As long as you can justify your activity in terms of what the company expects you to either do or be able to do for them, the management is not enclined or likely to look further into what you're doing and saying.
I would think it is good practice to invest company time in own development. As long you really do it only if you have not more important things to do (anything generating value for the company is more important).
Where I come from it is not expected to educate yourself in your free time, so doing it in office hours is the only education I get ;)
When you say "personal Project" please make sure that it is really close related with a skill or a knowledge you really need for work. As your boss I would not pay you for doing some side project which does not add any value for the company or your knowledge of work-related things.