Your friends need some taste! =) Greys are a wonderful color scheme, very fresh and modern yet with a classic feel. Here's an outline of some things I would recommend.

(1) Paint. Use rich greys, with a slight brownish cast. Steer away from blue tinted greys unless you are going for a blue color scheme. You can move in and out of lighter and darker greys for your various rooms while still keeping the same color. For instance a darker deep grey in a living room and a lighter version of the same color in a kitchen or dining room.

For a sleek, more modern look, paint the trim the same color as the wall. ALSO, I'm sure not everyone will agree with me on this; but I would actually consider painting your wood floor a dark charcoal grey. I'll give some links for some similar pics.

(2) Lighting. This is very important and can make all the difference in a room. Lean towards can lights, track lighting and new styles of pendant lighting. In your can lights or track lights use halogen bulbs or possibly L.E.D.s. Installing halogens in almost any light fixture gives a room an instant make-over; and the lighting is very flattering to furniture and humans alike. =) If you have any ceiling fans or lighting that is "frilly" or cheap looking, def rip it out and REPLACE!! p.s. I recommend Home Depot if you are going to be getting lighting from a home improvement store. They have a lot of new designs that are ahead of some of the others.

(3) Furniture. This isn't something that you have to do right away, but in time replacing what you have will make your look more put together. Choose your pieces carefully, remembering that "bigger is better" and "less is more". It's better to have several well chosen pieces instead of a whole bunch stuff packed in. A simple square leather couch or armchair would look good with your colors, and choose a few pieces that have dark, rich wood tones. Mixing up the paint with wood, leather, and possibly stone is restful to the eye and adds richness and dimension. If you have an eye for the look you can find excellent finds at Target, Ikea or stores like Crate & Barrel or Room & Board. And don't forget Craigslist and Ebay! Of course there are many high end stores too and you could consider splurging on a few high impact items like a quality leather couch or enormous wall clock.

(4) Accessories. As you assemble your "pad" you'll get a feel for whether you want to keep everything in the grey color family or whether you want some splashes of color. Either way, don't forget to add texture and pattern to each room. A soft rug contrasted with hard flooring, a striped pillow on a solid couch...mix things up! If you want to have photos displayed, reprint them in black & white, printing larger ones on "canvas" where they wrap the edges around a hidden square frame.

I think you're well on your way to an awesome spot...which hopefully will be greatly enjoyed by you and anyone lucky enough to be invited over!!