I've been going to the Italian Riviera every year for a few years now and I agree with everything here - its got to be some of the best riding in Europe right now. I stayed at Finale Freeride as a guest in 2010 in one of their 1970's caravans (a good cheap way to stay in town - check with Silvia if you need accommodation) and ended up doing quite a few weeks of guiding over the next couple of years.
May is definitely the busiest month but it drops off pretty quick into June so you may have better luck with shuttles. The place is huge with German speakers and they tend to come down in groups and book out shuttles. If there's just a couple of you it may be hard to get on one but its always worth saying hello to Silvia and Mark and leaving your number - they get quite a few cancellations most mornings.
If you're riding up then there are 4 enduro style trails up in San Bernadino which are easy to find and take you back into town. About a 250m climb on tarmac with a nice bit of singletrack at the end. If you're going to climb all the way to the NATO base or Cafe Din where the shuttles drop you then check out the Isalo Ecstasy or Crestino trails as they are more all mountain-y and you get more bang for your buck for the 1000m road climb you just did.
Other trails close to town worth doing are Brigga, Caprazoppa (the mental stage 2 - don't do it in the wet!) and Noli (the only good trail down to the sea).
BUTTTT! as swj77 says the Defender tour is what you really want to get onto. With a modern 6 inch bike you can rip the open corners like no other place I've been to. The trails have been built by Finale Freeride in the last couple of years, largely on their family's land so the trails don't get ridden out like in Finale. Its quite a long way inland but the Bormida and Osiglia valleys are absolutely beautiful. If you need to make up numbers to get a tour going maybe approach some randoms in town, I think you need 6 or 7 for the tour to run.
Definitely take a full face and run something like the Specialized SX / Schwobbly super gravity / EXO case tyres as the terrain is super rocky and you save a few hundred grams over a full DH casing.
If you have some shuttle assist Finale has maybe four days of riding before you start to repeat everything. With 2 weeks I would definitely spend, if possible, half your holiday up in Molini with Ady and Jo. The riding is so different but just so insanely good. 1000m vert runs through the trees are all over the place. The valley sides are steeper than the more rolling coastal mountains so you tend to get Alpine/Spanish style switchbacks rather then fast open corners but there are still loads of places you can get loose. The valley Molini and Triora are in is stunning too, just dense forest as far as you can see, up until the alpine at about 1600m. The bar in Molini closes when you leave. If you're with Rich the guide this is at 4am. Agrifolio is one of the best trails I've ever ridden and the immediate valley has maybe 20 other great ones. For singletrack descents its way better than a place like Morzine and its why people keep going back.
AHH what am I doing in London all summer I'm getting excited just thinking about the place!