Paul, which languages do you speak? I'm envious!!!
Since I was born in Belgium: Dutch and French to start with.
At school, I learned Latin, ancient Greek, English, and German (the latter 2, I perfected myself, since the school program provides only the basics more or less).
Since I had the basis of Latin and French already, I very easily learned Italian and Spanish at a level where I can easily understand ANY talk show on ANY topic in those languages. Unfortunately, I haven't had enough opportuntity to practise speaking during the last couple of years, so I cannot call myself fluent anymore in that respect. From what I remember in the back of my head, grammar in the Roman languages was not very easy to learn.
The last language I learned really well is Russian. Since Latin and ancient Greek also have 6 cases, this considerably helped in developing a very systematic approach, because you have to know 12 forms for each word (6 for singular and six for plural and there are different accent patterns for different groups of words). I also know a little Japanese since my Karate teacher was Japanese. Now, I'm learning Mandarin Chinese and after that, I plan on doing Cantonese. No complaints about lack of communication, since there are plenty of people who speak Chinese.

P.S.: You have to use the language if you don't want to forget it. Actually, since I don't use Dutch (my native language) anymore, I'm already getting the "on-the-tip-of-my tongue" syndrom, the failure to retrieve words from memory. Instead, I tend to mix in Russian and/or English words, which I use a lot more often.
Everylanguage disclose you an intere way of 'seeing' and 'thinking' the world, or a new world altogether.
Yes, very much so. Knowing other languages is VERY interesting in more than one way. For example, I have found that sometimes you find "safe" ways to express feelings that would be too painful, too confronting, too shocking to talk about in your native language. Another language is not just other words you learn or other grammar; it's often a completely different culture and other dimensions, images of everything. This fascinates me too.
Paul