Pages disappear from catalogs. Links go screwy. Watch for trouble, and resubmit if you spot it. The engines have grown smart enough to realize some sites only change content once or twice a year, so they don't visit regularly. Resubmitting every month or two will ensure that your site's content is kept current.
Some search engines take weeks or months before they update their catalogs.
For example, WebCrawler's catalog has been as much as 2 - 3 months behind. On the other hand, Excite's catalog consistently reflected changes soon after they were made, an indication that the catalog is constantly updated. However, recent reports reflect that they too are slowing down considerably due to the massive volume of submissions. For one thing, spamming doesn't seem to work with every search engine. The stakes will simply keep rising, and users will also begin to hate sites that undertake these measures.