As a long-time vim user switching to emacs (just to edit lisp code), viper mode does not feel very comfortable or familiar.
Sure, the basics are similar. But to get a good handle on how to use it and configure it to your liking, you have to read a ton of documentation. Also, configuring it effectively seems to require being familiar with many emacs concepts and ways of doing things.
A vim user is really going to be lost until he does a ton of reading on this stuff. And even then, it's going to take him a long time to feel comfortable with it.
And that's not to mention that by default viper only works in a very limited number of emacs modes. You can configure it to work in more modes, but then you'll loose out on a lot of default emacs features that are tightly integrated in to the regular configuration of those emacs modes.
You may be able to reconfigure those modes to allow them to be used more naturally in viper, but that's going to be a lot of work (and, again, require you to learn a lot about emacs).
So if you're a vim user switching to emacs, don't expect viper to make you feel at home. Vimpulse extends viper to be just a bit more like vim, but it's really just a thin gloss over the basic viper functionality. Even with vimpulse, some of the basics may be the same, but you're still going to be very far from vim.
And even if you do spend the time to learn enough about emacs and learn enough about viper to customize it to be much more like vim, you're still never going to be able to replicate one crucial aspect that makes vim such a joy to use: its thousands of plugins.
Sure, emacs has its own packages and extenstions that probably do many of the same things (arguably, for some of them, maybe even more). But if you use them you're going to be essentially just using regular emacs, with a vi or vim gloss over it.
If you're a vim user and you like, know, and regularly use many vim scripts and plugins, those aren't going to magically become available for you to use in emacs, even with vim and vimpulse. If you need any of the functionality of these extensions in emacs, you're just going to have to find the emacs equivalent and learn how to use it. This is going to be yet another major drain on your time.
Of course, if you're committed to really making a complete switch to emacs, it might be worth your time. But if, like me, you only want to use emacs for a limited subset of things, you're probably going to have to learn to live without the ease and convenience you get from your scripts and plugins you have in vim (unless you're willing to put a major amount of time and effort in finding, learning and configuring the emacs equivalents).