Timing
I measure both cycle times and shutter delay times, using a test system I designed and built for the purpose. (Crystal-controlled, with a resolution of 0.001 second.) Here are the numbers I collected for the Optio 550:

NOTE: My qualitative characterizations of camera performance below (that is, "reasonably fast," "about average," etc.) are meant to be relative to other cameras of similar price and general capabilities. Thus, the same shutter lag that's "very fast" for a low-end consumer camera might be characterized as "quite slow" if I encountered it on a professional model. The comments are also intended as only a quick reference: If performance specs are critical for you, rely on the absolute numbers to compare cameras, rather than my purely qualitative comments.

The Optio 550 is a bit of a mixed bag when it comes to speed, as it starts up and shuts down somewhat slowly, and it's full-autofocus shutter lag time isn't too impressive. On the other hand, it's much faster than average from shot to shot, and has a healthy buffer memory, with room for 5 frames at its maximum image size and quality setting. It's prefocus time is quite fast as well. Continuous-mode cycle times are a little sluggish given how fast it is in other modes, but the large buffer is a plus. Overall, a pretty fast little camera, particularly in prefocus mode and from shot to shot.

Power
The Optio 550 uses a single (fairly hefty) lithium-ion battery pack for its power source. The table below shows the Optio's power consumption in various modes, and approximate run times for each, based a single lithium-ion battery pack with a (true, not advertised) 1800 mAh capacity:

Storage Capacity
The Optio 550 stores its photos on SD/MMC memory cards, and a 16MB card is included with the camera. (I strongly recommend buying at least a 64MB card or larger, given the 550's high maximum resolution and conservative JPEG compression ratios.) The chart below shows how many images can be stored on the included 16MB card at each size/quality setting.