Simon's is definitely worth checking out if you are in the city. As to the latte art question- it depends now. I've been less satisfied with their consistency (not of latte art, but of quality). Simon still pulls a good shot, but some of the new hires are less than great.
In recent months,
Taste Coffee House in Newtonville has caught my eye. Nik Krankl took over the place in March and it has grown from a decent shop with a passionate owner to an exceptional shop with an extremely dedicated staff. They are pulling a coffee by Barismo on their Synesso, and frequently have a guest bean as well. Right now I feel that it is the most consistently good shop in the Boston area. It is definitely on par with many shops in New York (and better, in my opinion than quite a few of the big name shops there).
You might also check out
Cafe Fixe in Brookline (Washington Square to be precise). They have a Mistral and use Barrington Coffee (which is too dark for my tastes, but is liked by some apparently). Additionally, they have a pourover bar with a fabulous per cup program with Barismo coffees. The style of the shop is very similar to that of Ninth Street.
I second the comment that Bloc 11 is more consistent than Diesel, but I don't frequent either.
Other popular shops in the area include 1369 (in Inman and Central Squares), Crema (in Harvard Square), and Hi Rise (also in Harvard Square), though I haven't had especially good experiences at any of them.
Barismo's roastery is a sight to see (and a great place to talk coffee). Their hours, if I remember correctly, are most days from 12-6. They frequently host Saturday events open to the public. They are the real deal, when it comes to coffee.
-Ben