Back when I was working for a real estate company, I was also contributing vehemently to a tech magazine. It was a little bit weird keeping a day job and then running off to the other office (I was only paid per article. This was mostly labor of love) at night for editorial meetings. The thing was – I didn’t hide the fact that I was a contributor to a magazine. It’s not like I promoted this passionately within my day job, because that would be imprudent. What I did though was let my supervisor know that I was indeed writing, and she even suggested that I contribute to the company newsletter.
Nowadays, the concept of “conflict of interest” can be vague especially since information can be spread violently through the Internet. I guess my contribution to Migs’ post is that it really depends on what you want to achieve. Full disclosure is always an option and I would encourage that too so at least you are engaging in other activities in good faith with your employer. Remember, render to Caesar what’s due him and render to God what belongs to God.
There are of course, some exceptions to this. Example: If you work for a telco and were invited as a blogger / writer (your “sideline”) to cover a competing telco’s product launch, that’s a definite no-no.