I'll chime in about tire liners...I use them, and love them! I use the "Stop Flats 2" brand. I also ride a Cannondale Synapse (just got it actually!). The Stop Flats 2 liners I use are the orange ones, which are for 700x23 road tires. They go in between your tube and the rim, and so far they have worked flawlessly for me.

As for tires, I swear by Vittoria Rubino Pro's...they came stock on my previous bike and I rode those (with the liners in) for about 5,200 flat-free miles. I would not hesitate to get them again.

On my Cannondale, the stock tires are Schwalbe Ultremo DD's...which seem fine, but it's way too soon to tell.