I can see what your picture shows, but I'm not convinced that Timberline is hurting for snow at the moment.
I skied Timberline this last Friday (May 25), Saturday, & Monday (Memorial Day). It seemed to me that the conditions were very good for this time of the season. Was on brand new skis (Nordica Speedmachine Mach 3s) and wasn't the least bit concerned about the possibility of rock damage to them.
I don't know what the snow fall statistics are for Timberline the 2006/2007 season. However, Crystal Mt get's nearly the same weather as Timberline and they're reporting nearly 100 inches more this past season than their average (see www.skicrystal.com
I've skied Timberline this time of the season several times in previous years, and I would want to believe that they're in pretty good shape for the upcoming summer season.
By the way, I was shocked at how short the lift lines were this last weekend. Memorial Day was awesome skiing up there. The snow froze up really good Sunday night and they did a great job of grooming it. Keep in mind that the only thing up there is skiing on the glacier, which is basically a large groomer. The trail map shows the Palmer snowfield as a black diamond, but really compared to other resorts it's a steep blue run (perhaps other resorts would call it a "double blue" run).
As soon as school is out, the place will be packed with kids attending the summer ski camps.
Having said all of that, and keeping in mind I have no way of comparing the quality of summer skiing at Timberline vs Whistler/Blackcomb (haven't skied Whistler/Blackcomb this time of the season), I would pick Whistler over Timberline because of the village and all the other things to do there. (I live 90 minutes from Timberline...)