i have 1500 (!) contacts in php address book, and everything works great except the new ajax interface is much slower in looking up a name. under the old version, i could type in the name, hit enter, and it would find the name in a second or so. under ajax, it appears that something happens for each letter and this slows things down substantially (approx 10 seconds to type in a known name, wait for ajax, and get the results. )
this wouldn't be that much of a problem but as the search is working, it locks the browser.