It's a difficult one to answer because Hubspot is a continuously evolving platform. What isn't working so well today will be great tomorrow. The speed at which they are developing is mind blowing. I've been watching this now for 1.5 years and it's pretty amazing.
They're doing some pretty cool stuff and constantly pushing the boundaries, I wouldn't want to single any one thing out, none that might not be 100% of the parts will remain so. I just don't know in which order they develop but I know they have a team behind every aspect and like I said keep evolving the product.
So if the question comes of whether it'll be a problem because perhaps there is something that another software might be better in, it won't be long before that's no longer true. Buying into Hubspot means buying into constant change and evolution - that by itself could be a bit of an issue for some people but in my books that's their greatest plus, despite the constant learning curve.