We had a similar issue w/ our original vanity plan on the floor plan for our house. I did not want a huge long counter like that because I didn't know what to do with it and because I didn't like the aesthetics of this oversized granite piece in the bathroom. We looked at several solutions:

You can do different heights so you have a makeup vanity area.

I don't wear makeup so I put in a little window seat that people could sit on when they are drying off from the shower, putting on socks, etc. On the other side, we also put in a linen closet to shorten the vanity.

I think varying the heights helps a lot to add interest to the vanity and there are so many things you can do with the extra area. I'm putting in a lowered section so I can sit when I dry my hair. (I have a bad back, so I prefer to sit.)

My vote is definitely for a lowered section/make-up area, or some other way to break it up. We have a 7' double vanity in the kids' bathroom, and even with drop-in sinks (Kohler Archer, and those things are pretty massive looking!), there is a looooonnnng expanse of granite. I can't imagine what a single will look like in there. Plus, it's not that easy to find pre-built in that size. If you're going custom, it's also hard to make that long of an area look like furniture without it looking like a wall of cabinets.

We have a 9' vanity in our MB, but it has two sinks and it's higher than standard (39"), so those might help make the proportions look better (and no one sees it but me and DH.) Personally I love it -- lots of storage. Getting a granite slab long enough was no trouble.

I don't sit down to do hair/makeup so I didn't do a lowered vanity area, but they do look nice. (That lowered area on the left end is a storage bench; I get up early to work out so I keep workout clothes in there so I don't wake DH.)

We did one big mirror over the sink. Since then I've seen framed mirrors over vanities and those look very nice. If I had thought of that I probably would have done that. Other things that might help break up the look of a long vanity: vessel sink, basket storage, sconces on either side of framed mirror (see 2nd picture.)

Finally, you might want to post your bathroom layout and questions on the bathrooms forum. I've seen some really nicely done bathrooms over there with "wish I had thought of that" features.

Here's a pic of ours if it helps.
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Vanity with vessels and baskets and framed mirror (not mine but I think it has some nice features):

Here's a thread from the bathrooms forum that shows a vanity with a cabinet and pony wall next to it. I've always liked the look of this vanity (built by a contributor to the bathrooms forum) so thought I'd share it in case it helps. I don't know how long the counter is, but you can see how the framed mirror, vessel sink, different heights, trim, etc. really make the space nice.

Here is a link that might be useful: Vanity with Pony Wall

If you don't have a linen closet in the bath, you could add one there. I prefer to stand and reach IN to fetch items, rather than bending to drawers or shelves under a vanity counter. We have tall, deep, recessed medicine chests above our sinks. They look like framed mirrors, flush with the wall. Our lead carpenter made them for me.