They don't stack. If you have 10 feats that require a reserve of 2 points each, you only need 2 points.
Note that in the oncoming Extended Psionics Handbook (due next month), which updates Psionics to 3.5, this mechanic is done away with. Characters with few power points (Psychic Warriors) were restricted too much, while Psions can't care less whether they have to save 10 power points....
The new mechanic use the Psionic Focus. This is something you can gain with a period of concentration (not altogether short, though there is a feat to shorten it considerably). Some feats only require you to have the Focus to work, so you can them use all day, while others require you to "spend" the Focus. So if you spend the Focus on one feat, you can't use feats that require having or spending the Focus until you regain it through concentration.
Dragon has several articles on Extended Psionics, and the wizards web page also has a couple of sneak peaks, including the Wilder (one of two new Psionic Classes).
Other big changes to Psionics include the doing away with MAD (multiple ability depenency) - you only need one ability score for psionics now, int for Psions, cha for Wilders, and the other two aren't sure, though for the PsyWar it's probably con or str, and the other might be someting of a Psychic Rogue with dex, or something else with Wis - power scaling rules (all appropriate powers now list ways you can improve its effectivenes through spending extra power points, like one extra damage die for 1 pp, or a longer duration, or a higher save DC), and apparently they got rid of Psi-Combat.
[edit]Typo
