Valuations are high by historical standards, which means at some point they'll probably fall, but we're not seeing evidence of a fall yet.
It does seem to be getting harder to raise later rounds. But I think that is a secular change, not a market fluctuation. VCs seem to be shifting toward a strategy of spraying money at early stage startups, and then ruthlessly culling them at the next stage. This may well be the optimal strategy, but it's tough on the late bloomers.