As a result, the first person to view a page in a thread will trigger each post in that page to have its cache inserted into the xf_bb_code_parse_cache table.
This has the potential to increase the query count for loading that page by X where X is the number of posts you show per page.
On a board that I'm yet to upgrade to 1.2, that could be as many as 40 additional queries.
Although these queries only happen for the first person to view that page, and only ever happen once, I still wonder if it would be better to provide a cache rebuilder so we can run this ourselves at an appropriate time.
Personally on sites I'm involved with they're usually on big VPS' or dedicated servers so it's not an issue. But those additional queries happening at run time (as small as they are) could potentially adversely affect performance.