I've heard mixed feelings on the topic. Some companies such as Ebonite state to never use heat in order to restore ball reaction (they also sell a "compound" resembling kitty-litter that's supposed to remove oil). I called the Lane#1 customer service number and was told that it was alright to use heat... as long as you use some common sense such as not using too high of a temperature, no drastic temperature changes, let the ball cool down slowly etc. So depending on who you talk to, you will get different answers.
Personally, I have used "heat" on many different balls and never had any trouble with cracking, separating the cores, etc. My feeling is that once a ball becomes "dead" its of little or no use to me. As a result, the worst case is something happens and does by chance crack... I wasn't going to use a saturated oil ball anyways, so no big loss. When you see how much oil and other stuff comes out of a ball, its no wonder why they become dead.
As far as frequency goes, I would suggest (and stick to this myself), to get the oil removed at the same intervals as ball resurfacing. If you bowl at an older wood house, this may be as frequently as every 30 to 40 games (assuming you don't want to have a visible track on your ball and like a fresh surface). If you bowl in a newer house or on synthetics, it may be in the 60-80 game range (or when a noticible amount of reaction is lost). If you keep up with cleaning/maintenance, it should help prolong this.
S^2
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I think it's the duty of the comedian to find out where the line is drawn and cross it deliberately.
George Carlin
