We've extensively covered an issue where the MacBook Pro's battery gradually swells, -- apparently due to overheating. In mild cases, batteries swell but remain functional. In these cases, keyboard and/or trackpad functionality is sometimes affected by the rising of internal components.
In severe cases, the swelling is visually striking, and users are eventually left with non-functioning batteries. Sudden shutdowns while charge remains are usually precursory to such failures.
Our in-house MacBook Pro's battery has now fallen into the severe category, swelling significantly, with the unit shutting down routinely when running only from battery power.
Here are some picture of our swollen battery:
To recap, in most cases, Apple is replacing these defective batteries on an individual basis (our unit's battery was replaced without any haggling). However, the company has yet to disclose a manufacturing defect affecting any range of serial numbers or date-based production runs.
Anecdotal evidence (including our own in-house experience) suggests that the problem primarily affects MacBook Pros that were shipped early on in the production cycle -- our MacBook Pro was shipped in February.
For further coverage, see our MacBook Pro special report.