I'd say that highly depends on the type of software you're developing.
Imho easter eggs are more likely to be accepted (or even appreciated) in games than in business software. Even Microsoft had put some Easter Eggs into their products, but pretty much completely stopped that now. The reason why Microsoft stopped putting Easter Eggs in is closely connected to the possible reasons against Easter Eggs: security concerns. As outlined in the relevant Wikipedia article, Easter Eggs are usually (at least for the user/client) undocumented parts of the code which may lead him to believe that the product was more open to attacks or in other ways untrustworthy. Further, not all Easter Egg code is tested and audited to the same degree "mission critical" code is. That may lead to undiscovered flaws or loop holes in the code base which may be the origin of a later attack or malware exploit.
However, not all Easter Eggs are "bad" and require tampering with the actual code of the product. There are lots of ways to present Easter Eggs, especially in games where the code is somewhat separated from the content (game/graphics/scripting engine vs. actual script or level files). These ways range from special textures/objects and audio comments of the protagonist (e.g. as used in DN3D: Doom, Terminator, Indiana Jones, Star Trek) to secret levels ("there is no cow level") to dialogs showing when a certain object/location in the user interface is clicked, and much more. Of course not each of these is suitable for every type of product.
A nice way of putting an Easter Egg into your product is to include yourself somehow (and not only in the credits section). Blizzard did this very nicely with StarCraft 2. One unit portrait is actually the face of one of the developers. Something not-so-obvious like that is usually appropriate for many different types of software because it doesn't rely on media knowledge or a certain kind of humor. For example, perhaps you could include yourself as a character in the product's context. Depending on the product, this may not even require a chance to the code or only a very simple one.
Easter Eggs are imho nice but not required. The implementation of an Easter Egg should never detract from the actual product and its presentation should be appropriate for the indented target audience of the final product. An Easter Egg in a "serious" application or a product targeted at non-adults should never include adult humor or sexual content, no matter how funny or harmless it appears to be. This could not only lead to legal consequences, but also affect the marketing range of the software (USK/PEGI/ESRB ratings, for example).