"My coworkers and I were having a discussion about pockets being sewn shut on pants. One coworker was busily pulling threads from the pocket, trying to open it, and I mentioned that opening it might ruin the silhouette. Any insight into this matter?"
It really depends upon the style of the pants: Are they tighter and form-fitting, or are they loose and slouchy? In the case of the latter, by all means use the pocket. However, with the form-fitting pant, keep the pocket sewn shut. I know that bit of advice begs the question: Then why is the pocket there at all? It's merely there for the purpose of adding some visual interest. In the case of a functioning pocket, I don't believe that anything should be placed in it, unless that thing is as flat and unobtrusive as a credit card. As you so rightfully point out, we don't want to ruin the silhouette.
The Look of Love
"Do you have any fashion tips for a girl who's going on a first date with a man she's been friends with for a long time?"
It sounds like congratulations are in order, yes? And I assert that without an agenda. Unless you plan on showing a heretofore-unknown-to-this-man side of yourself, then you should dress as the person he knows you to be. I make the assumption that there are mutual attractions in place, so you — and he — are doing something right already. At the same time, context is everything. If this is someone you see only during the day and you're going out at night, then show him a dressier side of yourself. And if romance is strongly on your mind, then be a little more flirtatious than your style may normally be. Otherwise, enjoy being you and have a great time.
"I am from the Caribbean and will be attending an auction in London this month. I have some idea about what to wear — a pencil skirt — but I'm not sure what style top will work. Being of mixed descent, I prefer dark bottoms and color on top."
The pencil skirt is, by definition, fitted. Consider pairing it with a top that is fuller, such as something blouson and with a V-neck. It should be tucked into the waistband of the skirt, otherwise you will lose the positive impact of the proportional relationship between the two items. As for color, consider tops in deeply saturated hues like jewel tones.