I have to second this. The UI does suck, and the product is expensive ($65/user/month! once you cross 5 users, and $125/user/month if you want to use the API / build any custom apps), but it does scale very well as your sales team grows, and you start dealing with territories, quotas, etc.

It's also a de facto standard, at least in the enterprise space, so an additional benefit to us was that most of the sales folks we hired were familiar with it already.