I'm sure that other folks (like Moondog) would have more recent information, but I was there in April and while the renovations were present, it wasn't like it obstructed the key features of the sites

- Forbidden City - many of the buildings on the SIDES of the central courtyards were scaffolded and under repair... but the central palaces were all accessible and picture friendly. They also wouldn't let you wander away from basically a South to North walk through the complex (no side trips).
- Summer Palace - the large buddhist temple on the top of the hill was under repair, but the park itself was still very walkable and picture friendly. A few spots on the waterfront where repairs were being done.
- Temple of Heaven - again, some parts of the complex were being maintained (i remember the temple directly to the north of the main pagoda being semi-accessible due to some construction) but the main temple structures were all accessible.

In most cases, (other than trying to shoot 360 panoramas in one of the central courtyards at the Forbidden City), I don't remember being incovenienced by renovations. But then again, that was 3 months ago and in China, it seems like they completely overhaul their cities every year.