The servitor can manifest its presence in noticeable ways, similar to a poltergeist. Meaning: making things move, lights flickering, misplaced objects, etc. They can also effect the energy you feel, like a certain burst of cold or hot, tingling, that creepy "I'm being watched" feeling.
In the Chaos Magick communities I am a part of there are always talks of bringing a servitor to the flesh, which in general consensus is INSANELY difficult to do. You would have to pour energy into day in and day out. I see my servitors very vividly with my mind's eye, but I don't have much intent to make them physical. Then you have a whole new being that YOU are responsible for, like a child.
Once physical it would most likely rebel and want to leave you, so I just think it is all around a bad idea. Besides, I think that having an invisible entity to help you is much better than a visible one, for secrecy's sake.
People who are very 'aware' and 'psychic' may pick up on your servitor and be able to describe it to you.
I do believe it is possible, but I believe it would suck you dry of your energy or you would die of old age first lol. Think of how long it took you to become the being you are now... depending on how complex in appearance you've made your servitor (some are blobs, some scary, some cute, simple, detailed, it's really up to your imagination) you will have quite a bit of time ahead of you before it is full, physical flesh. Think of it on a scientific level: you would have to manifest each and every one of its cells, its atoms, its bones, whatever. Try to just manifest a fingernail, or a segment of hair, lol. If you can do that I'd say go ahead making your servitor physical... it really is your personal choice, I'm just giving you my take on it.
A servitor needs a 'food source', usually its creator unless specified otherwise. The more advanced and developed it gets, the more energy it needs, and like a child, or more accurately a servant or someone under your command, there will be a day when they realize they could easily kick your butt.
No I have never actually seen or heard of it done, but I suppose it is meant to be that way. I know I would never tell ;)