I just learned the trick (by accident, and luckily no spill) yesterday about the eye dropper top. As I paint in my basement (hence using only acrylics) I give them a good shake on the way down the stairs. I will definitely be popping a few tops off 1. to give them a good stir and 2. to clean up the dropper tops of old, dried on paint.
Yes, G-J, the colors do come close in a lot of cases. There are some where there is a notable difference (presently working on an FW 190 and their RLM lichtblau is quite far off from the decal sheet color chip), but with shading and weathering I'm quite confident this could be discounted.
All that being said, I think I'm pretty much sold on Vallejo paints and won't switch out. I find even their Model Air is very tough stuff when thoroughly cured.
One of the biggest selling points for me was reading how well Vallejo paints play with oil washes. After two or three days of drying I can use artists oils and some turps and I don't think I've ever had the turps effect the underlying paint. A big sell for pin or panel line washes if you use oils. Their gloss is beautiful stuff, I find it comparable to Future, and applied in nice thin layers works like a charm for washes or decals.
I also find their bottles quite cheap, really, and as previously stated, a bottle lasts forever (I'm still using paints I bought 8 months ago) so the economy is great. Personally, I'd recommend them highly, having used Tamiya and Model Master in the past.
As G-J said, they do make some very nice paints for figure painting (the Panzer Aces line) giving a dark, mid tone and highlight shade for most colors. I recently used their old and new rubber colors for a pair of aircraft landing gear tires, and it was exactly the look I was aiming for. Similarly with their flesh tone colors, they produce a beautiful range in skin tone that is easy to work with.