Your usage definitely does not affect your experience. MrBeep has confirmed this multiple times and I can attest from experience. If you were having issues during daytime I'd say it was more likely to be a line fault or congested exchange. Here's my usage for the past few months.
That's across two concurrent connections as too. I would definitely be considered a heavy user on a 1mb account. My download speeds are always great, my browsing is never anything but perfect and my overall experience is wonderful.
I would be very hard-pressed to find another ISP that can offer me this experience with this kind of usage. Not in the borders of this country, at least.